Using top vent without bolting down ok?

I've recently bought a old Jotul F3TD, a beautiful stove.

I intend on top venting due to my space configuration. The top vent flu collar bolts have rusted and broken off. It's expensive to replace the whole flue collar.

Do I need to bolt the flue collar in, or can I use the weight of the flue pipes to hold it in place?

The bolt mountings on the top plate are intact and I'll be buying a gasket for a good seal.

Thanks guys. I've done this. Saved myself a few hundred bucks in the process, too (also repaired the back vent cover).

I've also read in the interim that it's good to do bolt it down as it helps maintain a good seal in the stove.