Sad to see a tractor go when it has been on the farm a long time but there comes a stage when it get's to costly to maintain! Glad to see you sold her though.
Oops. It's been a long time since I did an oil change on the back end of a 690 so I cant really remember. Take a look underneath at the back, there will probably be a drain plug that you can undo with a spanner
It doesn't matter if you put engine oil in the back end.You can get universal oil that does both engine and hydraulics,I wouldn't bother changing it in an old tractor.