Head gasket issue with my '87 Park Ave ?

[DeaconBlue]

I recently noticed that my '87 Buick Park Ave with a 3.8L (3 code) V6 when the engine is warm and at idle (750 RPM) there are bubbles that appear in the coolant overflow bottle. One bubble, no bigger than say your thumb nail, approximately every 1 to 1.5 secs. I haven't yet checked to see if their rate speeds up or size get bigger proportionally with an increase in engine speed. But at that idle speed, it would seem to correspond to one specific cylinder's firing. The engine doesn't use any coolant and very little oil (much reduced consumption rate since I switched to Valvoline Maxlife oil). The car has a somewhat rough idle and bad initial throttle tip-in response. It can also be somewhat rough at curtain highway cruise speeds (especially noticeable since the broken motor and trany mounts were recently replaced).

Let me guess, bad head gasket with a leaking fire ring ? I haven't pulled the spark plugs or done a compression check yet. I hate working in a damp unheated garage in the Winter. Maybe that engine overhaul kit I pick up a couple of years ago on eBay just might come in handy ? TIA.