After a year of flawless use, the left downshift lever on my DA10 brifter is sticking. When I upshift (to the big ring) by pushing the brifter lever to the inside, the inner lever remains at the inward position when the outer metal lever returns to it's normal position.

Any thoughts? Will grease or graphite remedy the problem (if so, where)? I note that I don't recall this happening until after my bike was rained on.