Well, I dug this thread out to express the same problem...
Less than one month into using my brand new Tamron 70-200 and shooting with it less than 100 actuations, I came across exposure and DOF problems that just seemed odd. Knowing the sticky aperture lever was a common problem with this lens I dismounted it to find that it indeed was stuck and wasn't about to come loose.
So yet another fatality to Tamron's 70-200.... shame really, it's optically great and easy to use. Unfortunately the 6-yr warranty is US only
so I'll have to send it back to B&H and hopefully get an exchange.
Though I too am weary about just getting another copy that will eventually suffer the same fate, and next time beyond what would be supported by B&H's returns policy. Looks like I'll be asking for Sigma's version even though I'm not too keen on the brand...