Yea,

When I worked in a shop- we always put in OE plugs. So mercedes got copper core bosch plugs, Jap stuff got NGK's, Jags have Champions etc. I think it was the 930's which had the thick electroid plats which were expensive. Never had problems except stocking would have been easier with one companies product.
I understand at the user end, someone looks up a plug and it "fits". That doesn't mean it is equivlent. I seem to remember turbo cars had more problems with bosch platinums than others. Seems the platinum heat range(look in the back of the bosch catalog) is over a larger range than a standard plug. So, I'm guessing, it fit the size and range but was not centered and performance problems erupted.
blueEagle289. The M103 engine seems sensitive with it's ignition system. May not matter as much on the newer stuff,so your experience maybe fine for later engines... but not the M102/103.

Michael

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Michael McGuire
83 300d
01 vw A4 TDI
66 Chevy Corsa
68 GMC V6 w/oD
86 300E