Update - I've been continually adding makeup coolant to the overflow tank about a quart or so a week, and still no indications of any oil contamination or coolant in the exhaust. The leak appears to be limited to a slow leak from the front cylinder bank on the lower left (driver side ) corner that is vaporizing, on a few occasions I have seen and smelled hot coolant vapor over there, and some small wetting of the area on and adjacent to the starter, which appears to be drippage from above. Recently I started seeing the temp gauge spike up to about 210 degrees on initial warm up, and then settle down to maintain about 185 degrees where it usually sits. I did a level check in the radiator itself, and added quite a bit of coolant back in there, now the temp gauge is back to a stable heatup without any big overshoots, and when warm the rad hoses are a lot firmer than they were lately. I suspect that some air may have gotten into the system on one or two occasions where I let the expansion tanks level get too low.
I am going to get an estimate from my indie mechanic on the LIM replacement, however in the mean time I'm thinking of trying out using either Bar's Leaks or Blue Devil gasket sealer treatment of the coolant. I'm figuring that for a relatively slow leak like mine, it might work pretty well. A co-worker had a similar problem on a Mercury Grand Marquis that he fixed with Blue Devil and that fix has held up for about two years now. Anyone here tried these out? I realize that the best way to go will be the gasket replacement, but if I can resolve this with the sealer, I'm figuring why not? After all, they put Bar's Leaks tablets in the coolant right at the factory, at least that's what the techs at my local GM dealership told me.
Another question - at what point do the 3.1 SE (with A/C) radiator cooling fans come on? Most of my other cars have had the fans kick in and run continuously whenever the A/C mode is selected, and if the A/C is off, they will kick on if the coolant temp gets to a certain (usually a good bit higher) temp above the T stat setpoint. In the past I have turned on the A/C mode to start the fans to knock down the coolant temp if I've seen it creep up, typically if I'm stuck in traffic. When I tried that the other day when there was some temp spiking before I refilled the radiator, the fans did not come on. Perhaps because the outside air temp (about 20 degrees) was too cold? Before I put in the sealer and let the car sit at idle for about an hour afterward while the stuff sets up, I want to be sure the fans are in fact working properly . Will do a extended idle warm up test beforehand of course, but still would like to know the normal fan on and off setpoints.