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Hey sounds like you are into it now!! What size engine do you have? 1700 or 1800? I thought a web cam 78 was the one we should use?? But I'm no expert on that stuff!! They do say to use a web cam and lifter set!
I wonder still why the pushrod would move from the lifter? Could you have a spring issue? If the lobes are good and the lifter is good and the valve and valve guides look good what caused the rod drop in tension? So if the valve sticks in the guide shoudnt the pushrod still be in tension from the lifter and valve spring and return the valve to the close position?
Have you checked the oil pump also? I wonder if you got a oil issue in a passage and had a lube issue maybe a pushrod has a block inside?? So why don't you want to just split the case and check everything and then do a rebuild and be set? I got caught by that with my jug to head! I guess it does cost more and will take more time! I got the t4 dvd but it didnt seem to go over the measures like deck height, cc, ring gap, bearings, ect or lapping. Maybe there is an addition dvd or I miss that somehow?? I was hoping for more of that and setups combos options??
Hope you figure out why you had the problem so it does occur again! Hope it isnt a cam lift issue! bill

A couple things. Are these stock pushrods? If they are not stock pushrods and they do not have the correct tip geometry you can have problems, but usually on the rocker arm end. If for one reason or another....like a pair of rocker shaft nuts coming loose and allowing the angle on a non-stock type pushrod to increase....they can try to walk out of teh socket in the rocker. The retainer wires for teh PR tubes will drive the PR back into the rocker socket....but that momentary lapse will put the lifter end of the PR onto the "ledge".

Other things to look at, are the PR's straight? Also.....if as you are thinking...the valve guides may have been too tight, they can momentarily delay the closing of a valve. That can delay the pushrod following teh lifter downward. Then when it slams swhut the pushrod inner end lands on the ledge inside the lifter cup...causing the real damage.

I know its painful....but I would tear down the engine. Insituations like this...you may have damaged or lost camshaft end-thrust. Also bear in mind that if teh end thrust was somehow compromised already, striking an oil pump nut can do this same thing. Ray

The causative event was definitely a galled #2 intake valve guide (brass stuck to the valvestem is a sign of galling, and I've definitely got that), causing the valve to stick at max lift, causing the lifter end of the pushrod to fall down to the "ledge" on the lifter, causing the valve to open a bit more on the next stroke, causing the ding in the piston and damage to the pushrod and lifter. Yeah, they're stock pushrods, nothing fancy.

Good idea to check cam endfloat. I believe cam endfloat can be checked by pulling the oil pump and reaching in through a cylinder bore and moving the cam back and forth, measuring the endfloat through the oil pump opening. The only bit that is harder to inspect without splitting the cases is cam gear tooth damage. I believe I can check for excessive gear backlash with the jugs and oil pump out by turning the cam gear back and forth through the oil pump opening at various points in its rotation, but I can't look directly at the teeth to verify lack of scuffing or other damage. That's the judgement call right now, either pressing on after checking gear backlash and cam endfloat, or splitting the cases and inspecting the gears directly.

Be it noted that I have a leak-free case now (a good reason to leave it alone, though not as big a driver as others), and splitting the cases will put me far enough behind so I have to go work on the Duster again...shop scheduling at home is getting tight. Bench space is at a premium with two projects at the same time. Right now I'm OK, but in a week, the Duster engine bits come back from the machine shop, taking space in the garage currently occupied by VW bits. If I split the cases, I'd estimate a 4-6 week hit to the schedule, minimum. If I can get it out this week, I'll miss the Duster bits coming back from the machine shop needing a place to live. Decisions, decisions!