I've been looking around for the part number but obviously, I can't find what I'm looking for.

Can I use washers found in the local hardware shop?

and oh, I found this on ebay: Copper Washers 18mm X10 OIL Drain Sump Plug Gaskets BMW K100 K1100LT K1200 | eBay

Can I safely use it for the oil/coolant drain washer replacement?

thanks!