Reason was just to do the routine spline lube. Splines *looked* to be in good shape to me, but I have another spare final drive that I'm thinking to swap in and see if that works better, because yes, there was a great deal of red dust but also some grease.
Exhaust is all stock, so thanks for reminding me. Exhaust smells slightly sweet but there still could be some residual. I dont know how long anything sat previously, and there have been temp swings around here between 20 and 60. The exhaust smell is slightly concerning still, but I cant imagine where the two could be mixing. Condensation build up?
What was the reason for rebuilding the driveshaft? Did you inspect the splines on the shaft coupler? Was there a lot of red dust in the coupler, or just old grease?
Water pump won't put coolant into a cylinder, just the oil.
If it still has stock pipes, the exhaust mixes in the "goat's belly", so front/rear exhaust is all the same. I would lean toward condensation, especially if there's temperature swings in your area.