Far from sacrilege, given a couple of full screw thread rotations in the plastic, that’s a good idea. Would add some high temperature silicone as thread lock and sealant.
Thanks for the suggestion, but it's a fairly snug fit in the threads I tapped so I'm confident it won't come undone. The O ring acts as a sort of "spring washer" as well. But I'll check it in a few miles anyway.
