Hi Guys

Something and nothing really!
Can anyone recommend a filler for a gap between the back edge of an MDF sill
and uPVC window frame please?

Gap varies from 1 to 3 mm.

I am looking for a filler that will be long lasting (obviously) and
overpaintable.
Not too struck on using uPVC filler strip, but would consider this if filler
is simply not going to provide long lasting solution

TIA

Phil