Hydraulic valve

[reddawn]

I have an older wheelhorse tractor c-141, the hydraulic valve was leaking oil between valve body, I dismantled valve bto replace gasket, which turned out to be O-rings, In process of cleaning valve body, to reassemble I found small clear round gaskets or shims, not sure which they are, but my question is where do they go, and what is their purpose. Need help. THANKS