K&N filters are widely reported on the various Mercedes forums as the cause of MAF/MAS oil contamination from the filter. It's good to hear that you have had positive experiences with K&N on your previous Merc's. Just to be on the safe side, my personal preference would be to use the AMG recommended product.

Non resistor copper core plugs (only) are widely recommended on the various Mercedes forums to avoid problems on the M104 engine. Again, it is good to hear of positive experiences with the iridium plugs. But still, it is my personal preference to use the AMG recommended product.

Non resistor copper core plugs are getting harder to source I agree.

Google K&N Mercedes MAF MAS and also M104 and copper core plugs to see more discussion of these subjects.

Also see Mod "whunter" thoughts:

https://www.peachparts.com/shopforum/showthread.php?t=197392&page=4

Bosch Non Resistor Spark Plugs

It's been 25K miles since I've run the NGK BKR5EIX Iridiums in the C36 powered wagon (M104.041 engine w/HFM).

I've had no issues with starting (cold, warm, hot) in all weather (27F-102F), and I pulled them just to take look.

The insulator is clean & white, and the electrodes are SUPER clean. Gap is has grown from 0.032 to 0.033

I have a new set of Bosch F8DC4's waiting the wings, but I've read these Iridium plugs can go 50K miles.

My master AST tech was the one who told me these Iridiums are the only known working replacement to Bosch copper-cores.

He didn't recommend ANY platinums.