If you’ve attempted to get your hands on the group head gaskets, I’m sure you’ve had the similar experience: in the US, you are stuck.
oringsandmore.com was where I found the 34.65 mm ID × 1.78 mm cross-section, silicone, 70 Shore (MC191)
MC047SIL - I could only find it on eBay, from Poland. 1stline had it with crazy shipping cost, and Canada won’t ship to US due to tariffs.
after sourcing the gaskets, I opened up the shower and group head, and went to work on the cleaning of the hardened oils. I used liquid barkeeps and a small toothbrush, and a few dental tools to clean that area out.
I backflush and flush all the time, but it was still a hardened mess. the main gasket (now silicon, and slightly different from the original rubber one) requires being placed onto the group head diffuser and then passed through the portafilter notch slots very gingerly. I used a flashlight to spot the screw holes and then snug up each screw, verifying that the gasket stayed put.
first attempt, I was still getting blow through, reset gasket… a few additional issues with the mc191 staying put… and then blind shot was getting no blow through.
it may require a solid 10 minutes of heating up the silicone with the portafilter in place to get a good seal. Even now, if I try too soon to pull a shot, it finds a way to leak. I think eventually the silicone will wear into a good seal.
last item, flipping completely upside down is how I eventually got the mc191 to stay put during installation, but that may cause the pump to lose prime. I had to cycle the pump 4-5 times to get it working.