Hi, thank you for contacting JustAnswer.com. My name is Russell. I will do my best to provide the right answer to your question.
Please just tell me this much, before I advise you:
1. how old is the lens in question?
2. did you purchase it New, or Used?
3. has it always been like this, difficult to turn at one end or the range or all over the range?
Is it now difficult to turn only at one end of its range, or all over its range (awhile after you have cleaned it out with blowing again) ?
Has the lens been dropped or otherwise subjected to mechanical shock(s) in its lifetime?Has the lens been operated in or subjected to, temperatures below 32 degrees F (freezing point) or above about 100 degrees F ?Has it ever been subjected to a humidity higher than 85 % or gotten wet ?
It sounds to me as if the lens was defective somehow from the start.
Did the problem 'stay fixed' for at least a while after sending it off to warranty repair?
Sounds as if heat and low humidity dries it up or turns the lubricant in the joints to sticky powder - or something.
Having it repaired with that in mind, would be ideal. This is not something for the casual... be sure to tell the repairer, also, that you use it in various locales/climates/conditions.
This case may be returned to, at any time, at