generally 12-1500 miles is rebuild time on shocks, depending on how you ride it. if you jump alot and are real aggressive, you might need them rebuild sooner. if you ride mostly trails, and just "cruise with the family" kinda riding you can probably get alot more miles out of them.
before you say so, yes, there is still probably a lot of miles left on them before their shot.
notice i said start to get tired.
when you run a shock past the time it starts to get tired, it can potentially get more expensive than just a seal kit, and a nitrogen charge, the longer you run it. wear on components inside the shock itself starts to happen. if the nitrogen leaks out, as that is usually the first thing to go, then the oil getting out is also a possibility.
but its not really what can get out, that's the big deal. don't get me wrong, it is, but not as much as, if the oil can get out, water and condensate can get in.
and your shocks live in the snow, which is water. you cannot get away from it.
also, i'm with RJ, Hygear is among the top shock companies in the country. they know their stuff.
and where you send them, really depends on what you want done to them. if your just after a stock rebuild, take them to your local dealer, or a local guy. it doesn't take much brains to simply rebuild one. takes some special tools, but not much know how.
it's when you start getting into valving them for your weight and riding style that Hygear really shines. it makes a shock designed for your sled, and turns it into a shock designed for you.
if your going to keep the sled a while, i highly suggest having a valve job done, not just a rebuild.
i was quoted about $7-800 for 4 shocks rebuilt/revalved, 2 of those shortened 3/16", a pair of their triple rate front ski springs, a dual rate front skid spring, including return shipping. this including all seals and parts to do a normal rebuild. would not include things like if i have a dinged/rusted shaft or tube, things like that outside of a normal rebuild.
that also gets you free valve changes for the first few rides, if you need them tweaked. say you need them a tad stiffer or softer, or the first part of the stroke is nice and plush but you want the last part stiffer. you send them back, they will tweak them for free.
then, a year or two down the road, if you send them back to them to get rebuilt, it's free valving changes at that time as well. say you get 2 years older, and put on 30 pounds, you just got a free valve adjustment. their also a great company after the initial sale.
hope that helps.
99 zrt 800