Just picked up this thread related to gearbox lube oil - from what has previously been said it would appear that "lifetime fill" obviously does not mean lifetime or they would not put a filling and mt'ing point on the gearbox.

Oil analaysis is a very handy way of getting to know what is going on in the engine and or gearbox but you need a bench mark. What I normally do it take a sampl of good oil and them compare against used oil, this will show an awful lot as to the condition of the oil. Then there is interpretation of the results, this is where the clean oil analysis is handy. I use my local Caterpillar dealer for oil analysis, they charge but it's worth it.