M929A2 Hydraulic Reservoir Filler Cap Gasket

[gottaluvit]

Anyone know a good source for them? Here's what they had on mine and it leaks if parked with driver's side lower than passenger side. Seems too skinny and won't center on cap.

 

[gottaluvit]

Another question, I have some really good gasket material to make one but was concerned it could blow out. Are these tanks/reservoirs under pressure or just flow?