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Hi Dave, if the o-rings are in place I wouldn't expect some movement in the tube to be your problem. It sounds like you're aware of what goes wrong with the tubes already but just to be sure I've attached a picture. Check them carefully, if they're all good your problem may be with a cam or lifter itself. I assume your tapping is at valve speed, not piston speed.
Ok, if you have good oil pressure you might go ahead and try the new bridges but I think I'd warn the customer that it may not solve the problem. I'd also change the oil with 20W50.