Backscatter won't answer me on PT-059 parts information or sources either. I requested parts information from Olympus Support and they referred me to their Repair (OM Digital Solutions; the company Olympus sold their underwater business to in 2020). Their response was that the information is "Confidential". This tells me that it's a marketing strategy to make non-manufacturer repairs complicated/difficult and risky so TG-6 owners are forced to buy new PT-059s periodically when they start to leak through worn pushbutton o-rings etc. I'm done with Olympus housings and going back to Ikelite housings. Ikelite now sells a housing for the TG-6 for the same price of the PT-059 and they provide repair parts and repair service beyond the warranty period. Ikelite's parts support also enable's DIY photographers the capability to do field repairs on their expensive dive trips. Furthermore, the Ikelite system now has greater capabilities for the TG-6.
On the flip side, I've disassembled one of my leaky PT-059's to measure e-clips, screws, springs, and o-rings. So far, I've been successful on finding the two different sizes of e-clips and the three different sizes of small o-rings. Ordering, custom sized 316 stainless springs is proving to be too costly. Now, I've measured screws and trying to find the five different types and sizes.