With 2019 representing the 50th Anniversary for the Seiko 6139A automatic chronograph interest has never been higher for models based on this movement. Seiko also went on to release the closely related 6138A movement that added a second register to measure elapsed hours.
Seiko released a technical guide for servicing for their different calibers during the 70’s that provides information on the general operation, assembly and disassembly, and oiling points for the movement.
My example of the technical guides is a little yellowed with age, but is still able to be easily read. I have scanned the technical guides for both the 6138A and 6139A movements and have included these below.
Note: even if you only are servicing a 6138A movement you should also download the 6139A guide as the last couple of pages describe solutions for checking, repairing, and adjusting a slipping chronograph second hand when resetting a 6138A or 6139A movement.