Let’s start off gently here ….
Dislodging the “oil window” is almost unheard of, so first up, congratulations on setting a precedent.
I have no idea of how they’re set in there to begin with, but think “plastic onto metal” contact glue, and I reckon you’ll have a decent starting point. You’ll have to clean the contact surfaces of any trace of oil of course, but otherwise it should be fairly straightforward
This reminds me of an episode of “Black Adder”, where he was headed to America by ship. Upon asking for any maps on departure, he was handed a sheet of blank paper by a cartographer, with the suggestion that “If he could fill it in as he went along, we’d all be grateful”
Yer clutch – different ball game, and likely to be unrelated. From the symptoms you describe, my first thought is to check the return spring on the crankcase …..