Just wanted to share what I've found after experiencing my own personal cb550 round float bowl gasket hell.
Im trying to get the jetting right on this thing so the carbs come off and on all the time, also because Im too lazy to derust the gas tank so I have to clean them a lot. They leaked a lot too because I could never get the gasket to go in quite right. But now I no longer smell like gasoline :-). Not for that reason anyway.
here's what I have found...
1. Wrong part for the job -
The float bowl gaskets replacement parts for the cb550 k1 are just a round o-ring even though the bowl isn't shaped like that. The thing that sucks is that the groove that they are supposed to fit into is really shallow, so it's really difficult to keep them from springing back to their normal shape so they will stay in place. I didn't want to use grease to keep them in place because I was afraid of something clogging the jets.
Solution: part#SCI2634 at http://www.siriusconinc.com/pro-detail.php?pid=&product_id=1086
It says they're for a CB350, but they fit the CB550 perfectly.
2. Stretched Gaskets
Last time I cleaned my carbs, the gaskets were stretched out and pinched when I tried to reassemble.
I've cut the excess off before, but I don't think that's a very good solution. Some people say cut the excess and superglue them but I would think the gas would dissolve the glue and deposits could clog the jets. This time around I put them in a pot of boiling water for about a minute and they returned to their former size and once again fit perfectly.
Before I found that alternate part I was seriously considering putting 750 carbs on because of the nice flat gaskets.
Hope this is helpful to someone years after the original post...