Just an observation from my own experience: if you want to stop a leaking window for the long term, remove it and use the butyl tape or a good marine sealant/caulk. Putting stuff around the edge doesn't last very long, and looks unprofessional. I have one window that I removed' and sealed properly, as it leaked and I wanted to solve it permanently. The other one didn't leak, so I just put a quality silicone product around the edges for "safety." 10,000 miles of travel loosened that window up enough so it leaked in heavy weather.
Drilling out the rivits was no big deal; just drill enough to eliminate the "cap", push it through and pull it out from the inside. After you apply a sealant, the new pop rivits will be tighter and look nice, although you could use short bolts and nuts.
Good luck! A dry window is a great asset!