The guide rod adapter comes with a small washer as you know. Then with the GW spring they recommend you by a spring retaining washer to hold the spring, also. I bought it just in case. When i put it all on it just seemed like too much on the rod. I use only the guide rod and adapter and spring. No washer of any sort and it works fine.
Thanks for the tip. I think I'll try that 12# spring, too, and see how it runs compared to the 13# ISMI.