The problem is fewer and fewer dealers are keeping a readily available supply of "parts".
The last time I went to my dealer it was for a worrisome sound coming from the transmission. They kept the car for a day and came back with "Looks to be an issue in the transmission, our only option from Cadillac is just to do a module replacement for the whole transmission, that will be $17k". Once I stopped laughing I told them to button the car up and I'd pick it up. Within an hour of getting home I had a recommendation to a good mechanic who specializes in CTS and CTS V series, called them, took it in the next morning. By lunch I had a text "looks like it really just needs a good servicing and a new fluid filter, should be doable for around $225 all included, should we do it?" I told them to, picked it up before dinner, and problem solved.
That was the last time I talked to Sewell. Apparently they now consider everything broken down into key "modules" and they don't repair anything inside a module, it's swap and replace.