Anyone notice the replacement O-rings for the FW3A only fit the head end?

I got my forth FW3 a copper sand blasted and it had a funky switch so I took the tail cap off and dissembled and correctly reassembled the switch parts. While doing so I cut an O-ring or it was already cut so I grabbed the spare set. Both spare O-rings are identical while the light has two different ones head and tail. Both supplied O-ring only work on the head end. The tail cap O-ring is not as thick so the spares will not work. I also realized there is a second clear O-ring that is not the one on the black tube but in a second groove between the black one and the threads. I looked through all 4 boxes and they all only have spares for the head of the light. I guess it almost makes sense as you not supposed to take the tail cap off and I would not have if the light had been assembled correctly in the first place. Anyone seen this before? Know the correct replacement size? BTW I was a little let down as the light had a dark patina on it while still sealed in plastic. Not evenly distributed patina either. Must have been something in the sand used to do the sand blasting that was not cleaned off before packaging?

simply measure the dead o-ring and order similar size?

Yup that’s what I normally do but there are a half dozen or more almost the exact same size. Seems funny they ship spares that only cover 1/4 of the O-rings on the light.

Yeah, the clear o-ring in the tail is so thin… I lost it and after 20 minutes of crawling the floor I gave up. Luckily I had a spare one from the vape atomizer that fit perfectly. But it’s so thin, it’s pretty rare, I really don’t have another one.