Good News- Wasted money on Diff Fluid change- I think

New to me some months back, showing 85K on clock with unkown maint history although she is clean as a whistle and appeared well cared for. Decided to change F n R diff fluids. Pulled plug on front and it came out honey clean. BTW old trick learned from bikes which often share Gear, Clutch and Engine oil. Let sit as long as possible and when pulling plug let it weep out ever so slowly and examine first out fluid, any sediment would be present there frist. Fluid was consistent and clean. Same for rear. Would not say appeared new but who can say?

Suspicions-
At some point PO had fluids changed. Is that something the Stealership would have ordered? Not to commong for people to do maintenance items such as that. Is it possible that was factory fill fluid in there and still be very clean at 85K? I did not check capaicity of diffs but I put maybe .75 L in both ends. Pretty sure there was waaay less in there at drain than what I put in. Seemed maybe a 1/2 L came out. I used a very clean small container when draining so I could inspect fluid on way out. I did not accuratly measure but pretty sure it was low to start with which makes me suspect possile factory fill.

Side note-
Dang near impossible to check ATF fluid with dipstick as it is difficult to seat fully with the rubber O ring on dip stick installed. It takes a fair but of pressure to seat it. I removed the O-ring which made it easy to drop in fully and remove dipstick. Just don't forget to replad O ring when done.
Project for some day-
Find if the correct level is is in the pan or in the case, meaning is full at a level that is stil in the pan or in the case? I would like to have a plug I could pull and let any excess drain out instead of trying to add a bit without overfilling at drain and fill routine. It would just be so much easier to get it just a touch overful, warm it up fully and while at an idle pull the check screw and let it dribble out to correct level. I plan on draining and replacing every 30K or so. Other though is to pull a quart or so of fluid every oil change and replace with a fresh quart. This would be easy if there was a check level screw and I plumbed in a fill tube to the top of engine bay. Have a friend who has a Chryslar mini van used for delivery service, he usually gets 250 to 300k hard service on them before unloading and never had any tranny problems. He drilled and tapped two holes, one that was 1.5 quarts below fill level and other right at fill level. When changing oil pull bottom screw out and let some drain out. Put screw back in and add about 1.5 qts. bring up to operating temp and pull other scew, let dribble out and replace. Done, this would keep the fluid on a pretty clean basis at all times.