Window Sealer \ Paint Question

Ive just been informed by security downtairs that a parcel has arrived My vynal and headlinning kit

Now I will have to book my trimmer for next month and get my windows taken out.

I have noticed on the front windows round the seal there is some sort of black mastic sealer, what is the best way to get this
off when the window is out

Turps and or petrol.
Expect a mess

Cheers,
Ron