SF old E1L -tailcap rattling - KL1 worthyness

I've got an old E1L, with a KL1 Luxeon head, and the tailcap has developed a rattle when switched on. Any ideas as to what can this be, wether if it will afect function (not at this time, yet), and what can be done about it?

Also, I'm having doubts regarding the head. The Luxeon KL1 is a sub-performer, by todays standards, but it's very nice to have a TIR Surefire head able to take either one or two primaries 123 or a single protected battery (4,2V), with a nice tint and decent throw. Runtimes are kinda short, and brightness isn't stellar, although it is quite usable. Should i have it modded (no experience myself), or just ignore the short runtimes and use it at home with rechargeables?

Or I might just sell it to someone who wants to fumble with it, and get a different head for myself... I already have an E1L/KX1, an E1B and an L1, but I'm quite fond of the idea of having a single mode, single cell Surefire.

Is the switch a clicky? If so it's annoying but par for the course. You can lube it and possibly stop the rattle but it's a temp fix. It'll not hamper it's function or shorten it's service life with that rattle.
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IF you can get into it the mod is simple. And you can toss in a 20mm IMS reflector if you want something different.

I have 2, one with a heavy stipple reflector and a high CRI Seoul that puts out a very nice flood and the other has a smooth reflector and a neutral Seoul with decent throw. Runtimes on 1 cell isn't good like you said, it does improve some with 2 cells. I stuck a 2 stage McTwisty on my 2 cell and that fixed the runtime, I get the output of 1 cell with the potential for either higher output or a long runtime.