You can buy refill kits (eBay), which will produce excellent results if your drum etc. is still in good condition. My LW4/600 cartridge has been "re-fuelled" twice and is still going strong.

My advice, if you want to try it, is to wear a mask at the critical stages and do the deed outdoors at twilight on a reasonably still day, as there is some (dangerous) dust produced by the process, and as sun on the wrong part of the cartridge is fatal to it.