I got the kit specifically for the 5L. HP will provide the kit for free (or at least they used to), but I got it on eBay for a couple of bucks because it was much faster than waiting for HP to ship.

It's apparently a pretty common problem.

Re: fixyourownprinter.com - these guys seem legit, at least as far as the advice they dole out, though they can be pretty harsh on non-HP lasers. They sell a number of kits to fix various problems, but I have no idea of their relative price/utility, since I haven't had any of those problems yet.