Use it, care for it as circumstances allow, and fix it when something's wrong. And in that order.
1. Use it. It was bought to be used, so it shall be used. Not totally disregarding conditions, but not being stupid with it either.
2. Care. Wiping it dry if it gets drizzle on it. Not going from cold to warm, or warm to cold, but allowing the temp change to happen gradually. Making the bag it's stored in is also dry.
3. If something goes wrong, get it fixed... Still cheaper than a new lens. And, if they send back a quote to repair a lens that indicates it's not worth repairing, that's why it's insured. But I haven't had any real issues with lenses.
One place I have used for cameras in the past and that I would use again is
Camera Clinic in Melbourne, just posted it over. They could have done a better job at keeping me informed, like, "yes they received it", or "it will be a week" or "it will cost this much"... But they did fix it and they did know about it when I called, so I guess that's just how they do things. It's been over a year so maybe they've got better at communication.
Lots of other service providers too, here are a few links that I just googled up.
http://www.cameraservicecentre.powerup.com.au/http://www.canon.com.au/Support-Service ... ce-Repairshttp://www.ccdcameraservice.com.au/http://www.andersoncamera.com.au/http://www.cameracheckpoint.com.au/html ... rvice.htmlhttp://forums.whirlpool.net.au/forum-re ... 86877&#r10 (a list of service providers there)
http://www.maxwell.com.au/index.html (These guys used to be the Aus Nikon distributor, apparently they service gear too.)
Do a ring around and ask for a quote for a lens clean, quoting the same lens, see what you get.
One note from one of the sites -
Cleaning and treatment of optics for fungus, haze and other foreign matter is performed as best possible, however, complete removal may not be possible and residual marks may be evident.
So best to get these things serviced regularly if they are copping any sort of environmental abuse.