I tend to agree and I still and always read reviews and try to check out the sellers .. It’s a good policy to try and verify everything and everyone these days as best you can . I have now idea of the process of your purchase of the trans but it appears it involved 3 different businesses..I was ghosted for over 3 weeks before i sent the trans to Rockland.
After i replaced the trans i posted, that was another couple of weeks.
At this point i could care less what the seller or builder say/want to do.
If people dont voice problems then everyone keeps thinking things are fine. Who knows if or how many others have been screwed because they didn't want to cause waves.
I'm sure people will still deal with them, their choice based on the facts.
In the 50-60s they used heavy gear oil. Modern manuals use much lighter fluid.
ATF4
royal purple synchromax
Syntorque
Etc
T56 lubrication is based on a spash system inside the trans, 80-90 gear oil doesn't splash.
If you get the chance compare the location of the main shaft, the fill hole and then remove the 8 bolts for the rear case - 5th/ 6th and reverse all sit higher than the main shaft, 1-4 gears, fluid fill hole.
You made the purchase from Dan is what I think ,,, then after that it went to 2 others .. the rebuilder and whatever the other was ! How are all responsible for the trans ? The rebuilder appears to me to be the responsible party that took the trans from Dan to rebuild it .. That to me puts the ball on the rebuilder . Looking at the pics it appears to me that there was at the least something done to the trans ,, look at the , my guess some silicone squeezed out at the casing parts and some bolts I see also have definitely had wrench marks .. if the case had a crack and caused the leak of fluid then the rebuilder missed that possibly ! You stated you questioned the rebuild yet still went forward ,, That to me would have been a red flag at the start . Personally over my decades I’ve never seen a trans rebuilt that came filthy or not painted.. what vehicle did the trans come out of , was it a rebuilt core from who knows where ? Did it come from a wrecked vehicle ? There are lots of questions that I would want answers to before of putting down a large sum of dollars on any purchase . But without knowing the process of all the venders I have no idea how the did their businesses. I would be looking at the rebuilder as the first culprit for lack of a word !
As I stated my knowledge on the fluid used is not known to me ,, I will say gear oil 90 etc weight was used long after the 50’s and 60’s . I was an Auto mechanic in the mid 70’s and into the late 80’s .. all was gear oil. My 87 ford van and my 1987 both used the old gear oil .. I have a 2002 dakota but have never even checke the trans fluid or the rear end fluid .. I do and have change the rear end fluid on the 10 with the royal purple ! I’m glad you brought this more to my attention and I will be checking out the Dakota trans and rear fluids hahaha !
Now the question is have you fixed or replaced the trans now ? Or tried to repair the damage and possibly get up and running with a decent trans now .