I have a 70 - 200 mm f2.8L lens which I bought from eBay in USA. I was not happy with the quality of my pics compared to ny 70 - 200mm f4L lens (a lot lighter!). I brought it in to Canon at Harbour Front about 3 weeks ago. I got a call from them after a week saying that they needed to replace 2 groups of elements because of fogging and that the cost was about $500. I reluctantly agreed and when they called me 1 week later to collect, I was very disappointed that upon checking, my lens was almost in its original state - i.e. very badly fogged up, and obvioucly had not been serviced. The counter person took one look at it and immediately agreed with me. That was about 10 days ago and I'm still waiting for a collect call from them. It annoys me as I'm leaving for S. Africa in 1 week's time and would like to finish this episode before I leave. (BTW, I'll take the f4 with me becuz of the weight together with my 400mm f5.6L & the ext:bigeyes: enders.)
My point is:
1) They do accept lenses from elsewhere for cleaning and servicing;
2) It pays to check whether they have actually carried out the work that they are supposed to do.
3) Although the quoted price of $500 may be high, remember for that price you are geeting back an almost a new lens, with warranty at that too.
Only my 2c. worth.