In rereading your post it occurred to me the sight glass is for the hydraulics only (Blade,Bucket,Ripper).
The Dipstick for the reverser is located at ft.-center -floorboard - this sticks up above the diamond pl. an inch or two,is slightly over an inch across, and is screwed in, level is checked without screwing it in

Transmission is checked at rear- center of floorboards (between steering levers,at the back of diamond plate floor

I believe but am not positive you warmed up machine, circulated the oil, then shutdown on level ground to check fluid levels.

The Reverser also has a filter.
Filter is located on right side of reverser (just behind motor) look in the gap above skid Pl.(you will be kneeling next to track frame looking under upper section of track)The filter is under oval plate little over 4 inches in dia. held on by 4 small bolts.

Thanks to ccjersey ,art fro de leon,philip,one welder,dozerman51 and to willie for offers on tech manual I will pass all the great info to my neighbor and go from there. my sincere thanks....john~~~~~~~~~~~