Detroit DT12 shifting problems

What oil did you use?

 

Update: Tranny was dropped again and metal filings were found inside. It is worth noting that this unit has 800,000 miles on it. A rebuild was put in from a Canadian firm. 2yr guarantee as opposed to Daimler Rebuilt with 1yr. I tracked the old unit as I had the serial number and got in contact with the rebuilder and asked if they would let me know what they found. The dealer didn't even advise or document the rebuilder. I had the wherewithal to ask.
They did say the split pin was in the casing. Fault the dealer repair. But the play in the input shaft was significant. They said the opening was oblong. The 3rd gear was gone. Replacing might be your consideration as dropping these units out for any service is costly. You don't want to be neck in it in 12 mo. I also replaced the TCU at the time. Around $20,000 in November 2023 and I'd spent $8-9k in Feb 2023