This one has been running for probably over 20 years...
It is an AD, and I believe the AD does address the issue effectively.
But I wonder if anyone knows the reason, and particularly why the TB10 seems to have been far more affected than the other TBs. I have heard of just ONE TB20 which had the problem.
Reading this one http://www.sportaviationonline.org/sportaviation/201211?pg=34&pm=2&fs=1#pg26 you might ask to yourself whether AD shouldn't deserve some research before a course of action is taken for maintenance of your aircraft. I don't know a bit about your mentioned AD, but personally totally agree with Busch's approach to maintenance, even when AD are concerned.
I know nothing about this AD.
I would have expected on discovery of a corrosion issue Socata would have put something in-place like better corrosion protection to solve the issue.
Do all the TB series have the same corrosion protection? Are most of the TB10s components build in the same time period?
I used to work for a Socata distributor back in the late 90's and early 2000's and saw plenty of servere main wing spar corrosion on both TB20s and TB10s with the worst on a TB20. The root cause of the corrosion was poor heat treatment at production of the main spar leading to intergrannular corrosion. The nature of this type of corrosion means no amount of paint or corrosion preventitive compounds will help as it starts at the alloying grain boundaries inside the material.
The good news is that Socata always managed to create a repair solution but the drawing alone was in excess of 10,000 euros before work commenced.
As far as I remember the S/N's indicated aircraft manufactured around 1985 seemed to suffer most.
I'm not aware of a DGAC or EASA AD though but it's been a while, mainly surrounded by Globals and Learjets these days.