Hawkeye, since your car is the twin of mine, the “free” repair has probably expired.  That said, I would still push on your dealer for what they call “good will” repair help, which are free/reduced repair costs that Cadillac ends up reimbursing the dealer for (I know this existed before current Cadillac president Johan but I don’t know if he backs that anymore).  The argument would be this is a known problem to Cadillac & they should take care of it for free (1st approach) or at a reduced price (second approach).  I always found it cute that Cadillac sent out the TSB with 10 year coverage at a time when the ten years was pretty much up for most owners. 
If the above works, maybe you can split the $820 with me & Cubby!