I replaced the radiator and all the coolant about a month ago, using the Prestone "mix with anything". This weekend I will do a tear down, planning to replace the UIM and TB gaskets. I'll pick up a new set of LIM gaskets as well to have on hand.
It was cold out this morning when I started her (30s) and I had white exhaust, which made me think I had coolant in the combustion chamber (it went away and I had clear exhaust eventually). She does burn oil (166k) so maybe the coolant is mixing with the oil and burning that way. I'm pretty sure I would know if I had blown a head gasket (I still have plenty of acceleration). I can't find evidence of coolant on my dipstick on in the oil filler hole. When I replaced the radiator, my coolant was scuzzy - I assumed it was because I had a small crack in the radiator side tank, and the system was getting contaminated that way.
At this point I'm hoping that the UIM is the problem, and that coolant and oil are mixing a only a little, and that the regular oil burning (either rings or valve seals) is how the coolant is getting burned as well. What fun!