I hate to say it but I don't see anything wrong in that picture.
The wear area of the cam looks good and the small in focus area around the one visable spring has no build up other than amber color, which I would expect.
If you wish to double check the engine number send me the chassis number and I'll find you the original engine number.
Your first statement said the car was checked and "valve seal" found to be a problem. If the 750 included this repair I presume it was botched if you still use oil.
Bosch Master, ASE Master, L1
33 years MB technician