It is sealed and responds to vacuum signal just fine. What you see is what you get.
Vintage Sun Electric U-808 Tach Dwell & U -802 Vacuum Leakage - Not Tested
Vintage Sun Electric 1115 Vacuum Pump NOS Thomas Ind. 2107CA14 18 840 1015 1400
VINTAGE SUN ELECTRIC CORP. VACUUM PRESSURE TESTING GAUGE No.0309-0093 W/HOSE
Vintage Sun Electric Sun Scope Pattern Pickup 1747-102 HEI Adapter 1747-101 NOS
Vtg Sun Electric Vacuum Gauge Engine Vacuum/Fuel Pump Pressure S-114 Made In USA
Vintage Sun Electric Model 45 Timing Light Red Bakelite