Start up squeal usually is caused by the belt, not lack of oil. Check the belt, it may be shiny...the front shaft seal leaks oil/R-12 mix, gets picked up by the belt and flung off (that's the source of the greasy stripe on the engine side of the hood). In the process the belt gets shined up and squeals...same thing used to happen to power steering pump belts. If the AC shaft leak is bad enough, the compressor clutch gets saturated, and slips/squeals on start up. (brake cleaner sometimes helps cleaning the clutch). Good luck w/the indie. Old AC systems are a heart breaker.