Aluminum block should make a washer even more important, right? Without a washer, the pressure will push/bend the block easier and create a leak, right? Since it happened during the hottest days (105!), I think this is the case.

Since I only made a temporary fix this time, I didn't touch it. But if I have to replace the O-rings next time, I will definitely put a washer there.

I added one more can of 134 this morning and it seems holding. I measured the exit temperature and it's 37!