Ok, so I`m still stuck finding matching rings for the car. First here are some pics of the ring gap measurements I made:
I pushed down all the rings all the way to the bottom and meaured the end gaps with a feeeler gage.
Here`s the result:
I couldn`t find specifications for this particular car, but based on other German cars with similar bor size (e.g. BMW) they are way out of specs. The side rails for the 3rd rings look pretty badly worn in particular:
I`ll do proper measurements for the wear with a bore gauge once I receive it from Amazon. The bores look fine though, and I think a fresh ring set will make a big difference. Problem is, I can`t get one for the 2.5L engine. There are available aftermarket sets for the 2.7 engine, but they are listed as non-matching for the 2.5L, and I don`t really understand why, since the two cars have the same bore size (85.5mm) and the thickness of the rings seems to be the same too (1.5; 1.2; 2.0 mm):
Can someone confirm they are identical?