616 is not internally designed for a turbo, no oil jets and whatnot, but a number of people have done it, so that should work. Id personally leave it alone and move to a turbo 617 for fun though since its A, more powerful to begin with, and B, internally ready for boost in various forms. Or watch the 616 like a hawk during turbo service.
Lots of oil blowing out the top could be blow by, maybe just a valve adjustment. There are a number of threads on checking the blowby.
Not sure where the window relay as they describe it is, but 99 percent of the time, its the switches themselves that are bad. too much coffee spilled on them over the years.
I usually just check the fuse, then check the wiring to the motor from the switch for continuity, check that the switch is getting power, directly power the motor to see if the window goes up and down, and then once Ive proved to myself its the switch, I replace it and call it a day. Bad news is that the switches are 40-60 bucks.