problem is what is an OEM part??
Yes, TRW definately supplies parts to MB as do a host of suppliers.
Does that mean every part TRW makes that fits an MB are identical to what you purchase from the dealer?? NO. But, you'll find that miss-used commonly by aftermarket parts suppliers. Many times they have no way of knowing....
It's possible that the supplier sells in the aftermarket the similar part as supplied to the dealer/factory but makes it do different specs.
For your switch, maybe there is something that needs to be fixed causing the failure. Motor drawing too much current etc..
I buy lots of most of my parts from the dealership, but I get a discount. Hence, the dealership part can be cheaper, but ussually don't cost more than 10% more.
01 vw A4 TDI
66 Chevy Corsa
68 GMC V6 w/oD