There are 2 replaceable o-rings on the pump. A round fat one which seals the pump to the engine casing, this is where one of mine had a leak, I Just siliconed it as the wait and price was ridiculous.
And then the other is a thinner one which is large and seals the outer pump body to the main body, I just put a wee dab of silicone on it that as well.
1984 Honda CBX 750 FE
1985 Honda VF 750 F
1987 Honda CBR 1000 F
1988 Honda CB 350 SG