I have a Pioneer RT-71 in the basement workshop system. It's in pretty nice condition. Had it since 2012. I did belts and bulbs, clean/lube including FWD/REV switches and potentiometers. Have original box, owner manual and dust cover that required some corner repairs. I've never been able to find a complete service manual for it, even at the service manual pay sites. They are all just a few pages of circuit boards and a schematic. Some manuals in color, some B/W.
I downloaded a service manual for a T-6600 which is very similar. The RT-71 added a standard/LH tape selector.
EDIT: 01/27/26
FWIW, I got an answer from Norman at Analog Alley Service Manuals. (No affiliation).
He said it isn't a six-page thing, it's more like a large poster that was scanned into six pages. He explained that Pioneer are well known for not publishing duplicate material if it's covered in another manual. That makes perfect sense since the T-6600 is near exactly the same. The RT-71 just got a makeover, and they added the std/LH tape selector. He also mentioned on later manuals, Pioneer added the words supplemental or change. Sounds like my search is over and I may have everything that exists for it.