One more swipe at this, then I'll deny ever mentioning it.

I'm a former auto tech and shop owner and I'm against "jury-rigging" and "backyard mechanics."

However, there are times that you either "rig" or "toss" a part and this may be one of those times. No harm trying if you're not an airline mechanic.

If you have to replace a complex o-ring gasket and don't have a replacement, here's a workaround..........get the closest o-ring you can find and if it's not TOO short, use GASKACINCH brandname to hold the gasket into place while you put it together.

If the o-ring is just too small, buy 2 of them, then CAREFULLY cut the rubber at an EXACT square angle, put in the extra piece needed, then CRAZY GLUE the pieces together. Then use GASKACINCH to "glue" the gasket into the pump gasket groove and use extra GASKACINCH at the "joined" areas of the o-ring.

Now, I've used this method a number of times and it's even worked (for a while) on a small dirt bike motor.

The reason that I'm suggesting it here, is that there's no heat to speak of and using a bead of silicon to glue it, just won't work imo.

The reason I'm suggesting gaskacinch and not silicon sealer is that gaskacinch actually acts like rubber cement. You coat both sides, let them dry for a bit, then put it together and it's "glued" in place, making assembly dead easy.

Hope that helps

Used to have a sign on my desk: "Nobody has time to do it right, but Everybody has time to do it over!