Great! Thats not too far from me. I know now where to come for a really low miles, used bike when you want to sell!
I do ride quite a bit when the sun is out though, like today for example I rode for five hours, testing out my new S22’s
baby wipes work. or cheaper still, spray water on then place a kitchen roll sheet on then spray more water on, leave to soak, wipe off off dead flies and other road shite. Feed the jacket with Renapur Leather balsam and all will be one regardless of what colour it is. Welcome to the Forum BTW
Wet some kitchen roll, put it on the fly splattered areas, leave for about half an hour and the crud will wipe off. You control how much moisture you want to put on the jacket, but you should be able to judge how much is enough to rehydrate the remains so they just lift off.