cylinder head gasket
Depends on where you are as there are many good sources:
My favorites for 25+ years:
Bimmer Doc--Carl Nelson--800-466-88184
Mesa Performance--jim or spence--800-221-6372
Both are highly reliable sources for E-9 and all early BMW parts--have been doing business with them for many years--they are located in the hub of E-9 ownership in SoCal.