OIl level should be checked within 90 seconds after the machine is shut off and the oil is warm.
As for the chain case oil change, you could suck it out via the reverse shift actuator, loosen the bolts on the case cover/oil tank and drain it our the bottom, or just remove the cover / oil tank so you can get a good visual inspection of the internals. Things to watch out for: Top drive spocket bushing wear. I replaced mine at about 5k miles As it was getting loose. The tensioner roller is also known to have the bolts come loose and back out so many have tack welded the bolt to the tensioner arm.