Well, I don't think this really took care of the issue. Now I am getting some pressure relief through the drain when the lever is in the off position, but I am not getting complete relief--there is still pressure on the brew basket when I remove it. Also, the release of liquid through the drain valve seems less forceful than before rebuilding. So I am wondering if it could be due to one of several issues:
(a) I still haven't assembled the group properly.
(b) The cam and/or pin(s) on the preinfuse and drain valves are worn such that there is slight opening of the drain valve, but not full opening of the drain valve. The red arrows pointing to potential wear points.
Any thoughts or suggestions? Does wear of cam and/or pins commonly cause this problem? While I am guilty of using the machine for several months while having to force the cam into the brew position, I would be surprised if that caused enough wear to cause the drain valve to not fully open. If the answer is (b), I can solve by getting new valves and a new cam. If the cause is (a), I am stymied.