Not getting your rubber pinched as it goes in - a quarter turn twist of the tube as it goes in may help..and lube the mating surfaces with engine oil to help it slide in.
The sealing surfaces must be clean with all traces of sealant and any burrs removed from the tubes, head and crankcase, don’t use sealant when you install the O-rings and make sure the wire under rocker pedestals is located properly on the ends of the pushrod tubes. Are the pushrod tubes the correct length? Check that the O-rings are fully covered in the crankcase and head. This 2316cc engine is slightly wider than standard and I fitted spacers at the other end of the pushrod tube so the O-ring sat further into the head.
If anything, the thing I have to concentrate on is getting everything clean. Seating into the case end seems to be the the worst, though it could be slightly battered tubes. I put one new one in recently and thats not leaking, whereas the other three are.
