Service manuals that may come in handy.
Lens shutters
https://learncamerarepair.com/downloads/pdf/Mamiya-RB67-Lenses-Service.pdf
Pro S service instructions
https://learncamerarepair.com/downloads/pdf/mamiya-rb67-pro-s-repair-manual.pdf
Pro & Pro S parts
https://learncamerarepair.com/downloads/pdf/Mamiya-RB67-Pro-S-Parts-Catalog.pdf
PDF pages 1 - 5 of the service manual gives trouble and probable cause of the failure, a worthwhile read.
PDF page 13 of the service manual shows the cocking lever, shafts and gears involved in operating the cocking lever.
PDF page 11 shows how to check position of the cocking ring.
Lens problems 1 & 2 suggest the body is not cocking the shutter properly.
Lens problem 3 & 5 dead shutter, may not be repairable, #6 sticking levers in the shutter.
All shutters need a full Clean, Lube, Adjust.