LONG LONG TIME!!! I have had mine at least 6 years... no problems, a bit dirty... thats it, i check the rings every so often and had to tighten the screw on the front once, nothing else (i torch about 10 hours a week if that hepls) and I have had multiple different gasses used in bulk and 1lb canesters. The gunk thing happened when i used MAPP more than not... Also helps to bleed your lines! clean your torch with rubbing alchohol, and hang the line for a day or so to let everything run out (or if you are like me, and have no patients you can blow out the gunk with an air compressor! (and i pour a bit of alchohol in the hse too, and blow it all out.) good as new!
When this happened to me I really thought I broke it for good... to be sure i went to the hardware store and got a $10 torch that hooked up to my hose and let it rip... turned out to be gunk, not the torch.
this is a great link:
http://www.artglassanswers.com/forum...d66eb1d0c37c0c