Something been meaning to do for ages is to have the left sill off and clean behind it. Some years ago replaced the right one as previous owner must have bent it on a jack. Quite a lot of mud gathers behind the sill. Probably just as bad now, this was 4 years ago;
Got me thinking now. I think one screw at front, two at back and a row of poppers along the underside.
Then gently pull off. I wouldn't do winter, wait summer when the plastics give a bit.
