ETZ 250 front caliper question

[muddy]

I'm part way through restoring a 1984 MZ, got a quick question about the front caliper, as you probably know the caliper is in 2 parts held together with 2 large allen bolts. What's meant to be used to seal where the fluid travels from one half of the caliper to the other? My manual just says "packing", I'm assuming is should be a copper crush washer? But just wanted to double check.

[comanche91]

According to my parts manual, it's an o-ring, 7.5x1.8.