Even using 85A TPU as much as I tried, I just couldn't get a good seal on the jars, so I modified the body to accept a manufactured silicone mason jar seal. I printed the body on its edge with the valve mod vertical to get smooth faces for the jars, and cleaner center O-ring channels and it now works like a charm.

I have also included the tall up stem, shortened by 5mm; the generic mason jars I have are slightly too short for the originals.

Lastly, I have included a mold if you would like to try your hand at making your own O-rings out of a silicone sealant you would use on windows or bathtubs that would fit the original body (not the modified one I have posted here). The sealant I tried was a bit too soft, so I abandoned it, but perhaps it will be useful to someone else.

The link below is the jar seal I used. it's about 1mm thick in the middle and has a ridge on the inside and outside edges making them 3mm thick. The outside edge tucks nicely into a channel in the body and prevents it from moving or falling out, and gives the jar a very secure seal. https://a.co/d/58fHaQr

EDIT I found a seller on eBay who was able to make a custom seal for me that is a perfect fit for the original stüdenglass body. You can find it here: https://ebay.us/m/gO2qZk

Printer brand: AnkerMake

Printer: M5

Rafts: No

Supports: Yes

Resolution: 0.12 mm

Infill: 15%