Gasket genius: We need you now!

Remove m/c and belt sand the casting so its dead flat. Find a new oem gasket and cut up the old one. 1/2” wide seal ring off old gasket should work. Then put new one on and install cap. Will be a fight to get it locked in place but should work.

forgot, you have to wash the resevoir before re installing.

drive car. Realize it was a waste of time and upgrade the bloody thing already. If you are a purust, why the hell are you driving it?