I recently purchased a used Trek Madone 5.9. I had a local shop build it since it was broken done for shipping. They told me one of the shifters (dura ace 7800) was not working and that 7800 series was built so it cant be repaired.
I was told the issue was that the spring that pushes the shifter back to its normal position is shot so the shifter gets stuck. I dont know much about the components of these road bikes so i dont know whether i should believe it or not.
I would like to build a relationship with this local shop over the years and wanted to know if this is true or not.
Those shifters cannot be rebuilt. They can, however, get fouled from dirt and water penetration on the inside, and a good cleaning out can set them straight.
What your shop says is entirely possible. Shimano don't make individual parts and it is difficuilt to get into the shifting mechanisms without breaking them anyway.
When things get to this point, my last resort to stave off the expense is what I call the "Brake Cleaner Service" and the "TF2 Service". (Brake cleaner is a very harsh alcohol based cleaner made by Würth and TF2 is a common spray lubricant - similar materials may be substituted subject to availability). I've never tried but I think that a "WD-40 Service" could also be patented.
Each of these "services" involve squirting the named chemical liberally into the interior of the shifter whilst attempting to get the mechanism moving.
Cleaner/lube will usually go everywhere but (hopefully) in the process loosen the dirt or expell the water Alienator mentioned above. The long term effects of these chemicals on the plastic internals is not known (usually the shifter is on the way out by the time this method is used).
It has been known to work on occasion but should only be seen as a last resort.
