diff --git a/playbook/preinstall/preinstall.json b/playbook/preinstall/preinstall.json
index 60e08da..0e62096 100644
--- a/playbook/preinstall/preinstall.json
+++ b/playbook/preinstall/preinstall.json
@@ -138,7 +138,7 @@
       "Name": "UDC",
       "Installer": "UDC_Setup.exe",
       "Type": "EXE",
-      "InstallArgs": "\"West Jefferson\" 9999",
+      "InstallArgs": "WestJefferson -9999",
       "KillAfterDetection": true,
       "DetectionMethod": "Registry",
       "DetectionPath": "HKLM:\\SOFTWARE\\Microsoft\\Windows\\CurrentVersion\\Uninstall\\UDC",
diff --git a/playbook/shopfloor-setup/Shopfloor/00-PreInstall-MachineApps.ps1 b/playbook/shopfloor-setup/Shopfloor/00-PreInstall-MachineApps.ps1
index 04a737f..0536019 100644
--- a/playbook/shopfloor-setup/Shopfloor/00-PreInstall-MachineApps.ps1
+++ b/playbook/shopfloor-setup/Shopfloor/00-PreInstall-MachineApps.ps1
@@ -122,18 +122,21 @@ if (-not $config.Applications) {
 Write-PreInstallLog "Staged installer dir: $installerDir"
 Write-PreInstallLog "Found $($config.Applications.Count) app entries in preinstall.json"
 
-# --- Site-name override: replace "West Jefferson" in InstallArgs if site-config says otherwise ---
+# --- Site-name override: replace 'WestJefferson' (compact, no space) in
+#     InstallArgs if site-config says otherwise. UDC_Setup.exe expects the
+#     compact site name as positional arg 1; the spaced variant is used in
+#     other places (eDNC SITESELECTED MSI property) but not here.
 $siteConfig = Get-SiteConfig
-if ($siteConfig -and $siteConfig.siteName -and $siteConfig.siteName -ne 'West Jefferson') {
-    Write-PreInstallLog "Site config loaded - siteName: $($siteConfig.siteName)"
+if ($siteConfig -and $siteConfig.siteNameCompact -and $siteConfig.siteNameCompact -ne 'WestJefferson') {
+    Write-PreInstallLog "Site config loaded - siteNameCompact: $($siteConfig.siteNameCompact)"
     foreach ($app in $config.Applications) {
-        if ($app.InstallArgs -and $app.InstallArgs -match 'West Jefferson') {
-            $app.InstallArgs = $app.InstallArgs -replace 'West Jefferson', $siteConfig.siteName
+        if ($app.InstallArgs -and $app.InstallArgs -match 'WestJefferson') {
+            $app.InstallArgs = $app.InstallArgs -replace 'WestJefferson', $siteConfig.siteNameCompact
             Write-PreInstallLog "  Overrode site name in $($app.Name) args: $($app.InstallArgs)"
         }
     }
 } else {
-    Write-PreInstallLog "No site-config override for siteName (using defaults in preinstall.json)"
+    Write-PreInstallLog "No site-config override for siteNameCompact (using defaults in preinstall.json)"
 }
 
 # --- Machine-number override: replace "9999" in UDC InstallArgs if tech entered a number ---
@@ -310,9 +313,36 @@ foreach ($app in $config.Applications) {
                 Write-PreInstallLog "  Detection passed at $elapsed s - killing installer to advance (KillAfterDetection)"
                 try { $proc.Kill(); $proc.WaitForExit(5000) | Out-Null } catch { }
 
-                # UDC's installer auto-launches UDC.exe in silent mode. Kill that too
-                # so it can't write the placeholder MachineNumber to udc_settings.json.
+                # UDC's installer auto-launches UDC.exe silently; it's UDC.exe
+                # (not UDC_Setup) that actually writes udc_settings.json from
+                # the CLI args. Killing it immediately after the detection
+                # marker appears loses the MachineNumber write. Wait (up to
+                # 15s) for settings.json to reflect the target number, then
+                # kill. Works uniformly for tech-typed numbers and the 9999
+                # placeholder - whichever was passed as arg 2 is what we
+                # expect to see persist.
                 if ($app.Name -eq "UDC") {
+                    $udcJson   = 'C:\ProgramData\UDC\udc_settings.json'
+                    $targetNum = $null
+                    if ($app.InstallArgs -match '-(\d+)\s*$') { $targetNum = $matches[1] }
+                    $waitSec = 0
+                    while ($waitSec -lt 15) {
+                        if (Test-Path $udcJson) {
+                            try {
+                                $mn = (Get-Content $udcJson -Raw -ErrorAction Stop |
+                                       ConvertFrom-Json).GeneralSettings.MachineNumber
+                                if ($mn -and $mn -eq $targetNum) {
+                                    Write-PreInstallLog "  UDC persisted MachineNumber=$mn after $waitSec s"
+                                    break
+                                }
+                            } catch { }
+                        }
+                        Start-Sleep -Seconds 1
+                        $waitSec++
+                    }
+                    if ($waitSec -ge 15) {
+                        Write-PreInstallLog "  UDC did not persist MachineNumber within 15 s - killing anyway" "WARN"
+                    }
                     Get-Process UDC -ErrorAction SilentlyContinue | ForEach-Object {
                         try { $_.Kill(); $_.WaitForExit(2000) | Out-Null } catch { }
                     }
diff --git a/playbook/shopfloor-setup/Shopfloor/lib/Update-MachineNumber.ps1 b/playbook/shopfloor-setup/Shopfloor/lib/Update-MachineNumber.ps1
index 403f003..6b707b2 100644
--- a/playbook/shopfloor-setup/Shopfloor/lib/Update-MachineNumber.ps1
+++ b/playbook/shopfloor-setup/Shopfloor/lib/Update-MachineNumber.ps1
@@ -129,7 +129,10 @@ function Update-MachineNumber {
     # --- Relaunch UDC with new args ---
     if ((Test-Path $script:UdcExePath) -and $out.UdcUpdated) {
         try {
-            Start-Process -FilePath $script:UdcExePath -ArgumentList @('-site', "`"$Site`"", '-machine', $NewNumber)
+            # UDC.exe arg signature: positional compact-site (no space), then
+            # dash-prefixed machine number. Example: UDC.exe WestJefferson -7605
+            $siteCompact = ($Site -replace '\s+','')
+            Start-Process -FilePath $script:UdcExePath -ArgumentList @($siteCompact, "-$NewNumber")
         } catch {
             $out.Errors += "UDC relaunch failed: $_"
         }