My experience exactly with my 8 speed 105. After a winter lay-off it would go onto the big ring but not the other way. (Not that I use the big ring much.......) Once on big ring it wouldn't come off. One day, using the bike for the first time after winter 'storage', exactly this happened. I passed a house with the garage door open and stopped and asked if they had any WD40, They had and in a couple of mins I was back on the road.I and some of my mates have had trouble with STis especially the left one seizing after a period of inactivity. I reckon the factory applied grease sets. A squirt round with WD40 usually sorts it
Used that too when WD40 ran out, again no issues.I find GT-85 seems to work better than WD40 when freeing up my RSX 8-speed brifters.
Smells nicer, too.