Your SL66 looks to be in nice condition, I have also a Early version SN 2907xxx I bought mine at a local auction a few years ago, a local well known camera camera collector was down sizing (The auction went for 2 days !!!) I got mine at a good price and it is like new with original box and papers.and has never had any issues, it is my most prized camera. The quality of the images it can produce is amazing, I have compared it to a hasselblad ...... it is bigger and heaver but the more you use it the more it grows on you. The only problem is the some accessories are hard to find, if you do alot of flash/ studio work the 150mm lens with leaf shutter is good investment the cameras slow sinc issue goes away once you have this lens, another worthwhile item is a second film back, all the accessories for this camera are incredibly well designed.
Enjoy
Johnkpap