Ray,
I don't like to do salt in the wound - but may be you remember what I said you about this lens.
The real problem is - that a so lens with this range on high quality has to be sold for 3500 dollars. This is the real problem.
the material which Canon has to use to get the prize for this lens had to be on the lowest quality level. Just see the lock - this is the cheapest design which is possible.
Sorry for that - but in the base a so lens to the prize never can be a good value and quality......this is simple the fact.
The other problem is that the quality is so bad that damaged can be easily happend by very cold or very hot temperature.
Especially by cold temperature the plastic like the lock breaks very fast.
This lens was never for temperature extremes like Bonneville or cold winter in Salt Lake designed - this is also the fact.
At last - this lens was never produced for professional level - this is for standard user which not like to spent too much money but need once the year a long lens.
It is not necessary to move to Nikon - you will be not happy with this change.
The reason is, by Nikon the good quality cost you 30 percent more - and a proper cheap you will never get by Nikon.
You got a very got 7D body and this brilliant 100-400 mm lens - as I said you before - you have to spent some more money on the short distance lens - this will be one bigger bill for a good lens like the 24-105 lens - which is solid good design a proper value. If you like to get some ideas for the right stuff for you write me a mail - you know how you can get me
Don't worry mate - this problem with this lens was not you - in reality is also not a Canon problem - the real problem is the market from people, who like to get a Canon 500 or 1000 and don't like to spent the money for a proper lens.
Canon just fill the market with a product the customer crowed ask for - a sh.. cheap crap.........
What Canon's problem is, is the arrogance of the warranty issue - they know that this lens is crap - but they let customer pay the bills for that.......but, unfortunately Canon is not alone....you will get the same problem with all the other like Sony or Nikon......only that you have to pay more for the repair.......
So, Ray, head up......and let me know how I can help you.