Boler Window Rivets!

[Khan]

hello,
I am in a panic. Need some urgent advice.

I am a newb in renovation, and am getting our boler ready for the trip from next weekend. Last week I had success in installing the Brakes and a brake controller, so I got encouraged to solve the leaking window problem armed with butyl tape..

First surprise, rivets instead of screws. OK researched rivets, looks simple enought, ran to Canadian Tire and got assorted rivets and came back, and drilled the current rivets out.. almost lost it on some of the rusted ones.

Then to my surprise, the rivets are not squeezed in on the other side... they seemed to be held in with glue or somthing!!

Also the insite window backing plate has its own rivets not at the same place as the outside window frame, not squeezed in it seems!!

Is this normal?
Is this some kind of riveting technique that I don't know about?

I haven't found any advice or videos about rivetted boler window resealing.

So when putting them back in, should I squeeze the rivets?

Please help!

Thankfully yours:
Khan

[Khan]

By the way I am taking about the back left window