Conti twist or something else!!

On Saturday after 130 miles or so doing the Derby 150 with no issues I had a bit of a backend wobble in the wet then about 20 mins later riding in a straight line I lost it when breaking as a car turned. No major damage other then dented pride but don't know if it was the conditions, bad riding or if Conti's are poor in the wet. Only other thought is the rear shocker is fairly old but seem's ok. Any thoughts?
Cheers
Cheers