I sent in my DA*16-50 - a used copy that I purchased from someone local - after its SDM stopped working, with a letter explaining what was wrong, copies of its repair/replacement history and receipt from the previous owner.
There was no further communication from either side but within a couple of weeks, I had the lens back working like brand-spanking new, spit-cleaned and all, with an invoice explaining what was done.
The SDM failed on me again but that's another story
The service, I'd say, is prompt and excellent but why wouldn't it be? As they keep repairing their faulty equipment over and over, they must have gotten it down to a science