Is this the check valve? It's not clear what part you are showing us.

Tug,, It is very obvious those pictures are the contact or wear surface of said follower, and the OP mentions the lobe wear as well.

It is the combination of substandard materials as well as the lack of any decent EP, you know all the stuff that is being regulated out of existence.

It would be nice to have some very clear close up photos, and include the cam.

That's not so obvious because the contact area should be spherical. It isn't in these pictures. The part also looks very thin. It's not likely a bucket. This needs more explanation.

Some more pictures of hydraulic lifter:


Sorry, but I didn't take pictures of camshaft

Strange pitting pattern on the surface. Almost looks like it suffered an acidic etch. Any water in the oil?

I've seen some info on older Chevrolet engine flat tappet radius from 35" to 60", I have not researched any more to see which that is for sure.
On that small diameter lifter body you will not see the spherical effect of that in a simple picture.

You have 16 valve engine so I doubt it is a pre-'80s engine but take a peek at this OpelGT forum:

https://www.opelgt.com/threads/solid-lifter-wear-p...

Some comments on random odd lifter damage from pitting. The embedded Hemmings Oil link discusses some concerns with the reduction of zinc compounds in more modern oils:

https://www.hemmings.com/stories/2012/10/18/tech-1...

The lifter pitting you have really looks like an acidic attack. But why would it affect only one lifter of 16 makes me back away from that idea.

More likely it was a duff unit coming from a different production batch and even more likely a different manufacturer.

"Schiefgehen wird, was schiefgehen kann" - das Murphygesetz

Quote (Lou Scanlon)

More likely it was a duff unit coming from a different production batch and even more likely a different manufacturer.

Yes, for a 1 out 16 that is the most likely situation!

Spalling. Hardened surface cracking then breaking out in chunks.

je suis charlie

Brian Malone - no, oil is clear, any water in it. Sorry, I forgot to mention, it's 4 cylinder dohc engine

The first thing i can think of is indeed water in the oil. That may cause poor lubrication and thus excessive wear of the hardened surface.However, most times when water is the reason for the damage, you will find similar damage on all lifters. Thus the damage is due to specific circumstances with this particular lifter. A possible cause could be temporarily blocking of the oil feed to the tappet or indeed a substandard part. A lack of EP it certainly it is not - EP additives are never used in engine oil since the very high local temperature conditions necessary for EP additives to operate are never met in engines. A lack of anti-wear additive also is not very likely, given the fact that only one lifter is effected. More recent engine oils do indeed contain a lesser amount of anti-wear additive then in the past. However, modern anti-wear additives are much more effective then those used in the past and a lesser amount of additive nowadays will even offer better wear protection then previous types. And anyway - if the oil quality was the reason for the damage, it would be visible on all lifters.

I had beautiful dendrides formed on some followers with a new cam. It appeared to be a hardening problem with the cam.