Surefire KL1 intermittent failure

After a month or so of searching on here and elsewhere, I have yet to figure this mystery out. I have a Surefire E1L with a KL1 head (s/n of the head is A09402) that I've been using as an EDC for several years now. At first, I used primaries, then Powerizer LiFePO4's, then AW 3.7 750mAh RCR123's. Within the last few months, the light won't light up unless I give it a stout thump against something like a truck tire. Even then, this doesn't always work. I've ruled out the tailcap, because taking the tailcap out of the equation yields intermittent results. Has anyone ever had this happen? If so, what did you do? As it stands, I'm considering either a KL4 head or one of these http://www.opticshq.com/page/Optics/PROD/Surefire-Accessories/FL-TLS-TX2-1
I think I've become a little too attached to having a light with a hat-clip that has that good of a beam (when it works).

Don't know if this applies to yours, but I have a low serial number KL1 that had a similar problem. It turned out that the battery contact button at the bottom of the head had a solder blob that was corroding, causing intermittent operation. I first cleaned the connection, but the problem would happen again. The solution was to scrape all of the solder off. I have a KL1 with a serial number around A10800 and it has a soldered button so yours probably does too. Later versions I've seen have a solid metal contact with no solder applied.

Have you tried a primary cell to see if the intermittent issue happens then?

DimeRazorback said:

Have you tried a primary cell to see if the intermittent issue happens then?

Click to expand...

Not lately. I could've sworn that I had a primary or two (yes, Surefire brand) running around here somewhere. If I can find it, I'll see what happens.

By the way, george, where is said solder blob? directly underneath the contact?

I believe he meant the positive contact on the bezel. I have the exact problem as you and had just recently sent the KL1 to Surefire.