I have a 2005 Buick Lesabre Limited with 180,000 miles on it. We've owned it since new and had relatively few issues in the long run, Buicks are notably solid daily drivers and we've kept up on regular maintenance with it. Within the last two years I've been experiencing shifting issues within the automatic transmission around 1500 rpm when I first gain some motion in the car. It feels like the transmission stalls the shift, turning what should be a smooth automatic shift into a small but noteable jerk. A computer scan from a local mechanic turned up the transmission solenoid going out. Most mechanics will either want to replace the transmission entirely or quote it as not worth the effort to fix. Regardless, the mechanic stated he'd be willing to replace it for $600 which sounds like a solid offer, but also prefaced that in general its not a huge issue and I can still get a decent amount of use and life out of the car regardless of that fix. The question I have; is this fix worth it? I'd love to get as much life out of this Buick as possible but on the other hand, the cost to replace the solenoid is around half what the car is worth at this point. Would it be better just to ride it out or would it be worthwhile to pay up and get it fixed?

tl;dr: Buick Lesabre transmission solenoid is going out. With 180,000 miles and a value around $1200, is a $600 fix even worth it for a couple more years of use?