[Gelbster]

In theory you listen(with a 'scope) for lifter noise on the cam cover and piston slap on the lower part of the crankcase half. The problem would be if your bores are egg-shaped because of wear on the thrust side of the bore. You'll get some slap but there isn't much(inexpensive) you can do about it. The most appropriate engine oil may reduce the rate if such wear but .....
I like Jake's solid lifter because it eliminates (?) one source of problems.
It appears there was a design/tolerance/variation issue with the older lifters because some other cars that use the same INA/Schaeffler part had the same problem.
In my case all 24 tappets had honey colored oil in them. Despite that, some were jammed in the fully compressed position, some were 'soft',others were perfect. No debris in the oil ways, no abnormal wear on the lifter bores.Please note I said "jammed+fully compressed". New lifters are almost impossible to compress when they are correctly filled with oil. The new (BMW)lifters I purchased came in individual oil-filled containers. The funny thing is, they came airmail from Europe and I presume the pressure reduction during the long flight caused them to leak into the cardboard outer packaging. What a mess.