54mm Silicone Steam Ring Compatible with Breville 800 Series Machines Breville BES870XL Barista Express, BES860XL Barista Express, BES840 Infuser Espresso Machine, Duo-Temp BES810BSS Gasket

I purchased this seal after originally purchasing the green seal. DO NOT BUY THE GREEN SEAL FOR YOUR 870XL. This seal works great...no more leaking water from the group head.UPDATE: After pulling several espresso shots the group head started leaking again. The seal would only hold when the pressure was in the low range. Anytime the pressure was in the top third of the gray band, the seal leaked. After multiple issues with seals, I found a flush valve seal at Lowe's to use as a spacer between the group head seal and the porta filter. The inner diameter of the seal is perfect, but you'll have to trip the outer diameter, using the espresso machine seal as a template. It works perfect. It allows a nice tight fit of the porta filter and no leaking under pressure. While I shouldn't need a spacer at all, I've gone through three different seals and they all leak so this spacer solution is an easy, cheap fix.

This one from Caffewerks fits well and is able to stand the pressure of the cleaning cycle unlike the green one from MacMaxe which has many reviews but does not fit will and cannot even pull a shot which is much lower pressures than the cleaning cycle.