There was discussion on the SpecE30 and R3VLimited fb pages re. diff clutch disks and steel dog ear plates.
Summary.
Diff clutch disks might be pretty generic. So wherever you find them, they might be ok.
Dog ear plates are a little tricky. If you decide not to replace them, look carefully at wear on the dog ears. Maybe flip them over.
Some dog ear plates are being made of mild steel and they’re not durable. Thayer was mentioned specifically.
There is a Porsche dog ear plate that is exactly the same–even has the same part # on it. So don’t think of it as getting a Porsche part, think of it as getting a BMW part via Porsche. This link goes to the bf.c post that mentions it. The E36 Diff Thread - Page 7