Ingrained dirt on top sill

Good morning guys, as the title says, I don't know if I'm missing a trick. When cleaning top sills I'm having trouble getting ingrained dirt off the top sill. I use virosol sprayed on the brush, scrub it in leave and rinse off and it doesn't seem to touch it. Used cif on brush head with same result. Obviously I can get hands on doing the bottom sills, so they're not a problem. Any suggestions to give me a better result. Cheers and have a good day in the sun, if you've got any! 

How can you see it if its on the top sill?

No.I' not that tall. You can see the front of the sill!

Ladder and a magic spung with some tfr 20 or in really bad cases a washing up scrubber scerry pad with some pink stuff

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Thanks Tench for the reply but I don't do ladders! That's how I do the bottom sills.

I use a gardiners doodle bug pad holder and pad, enables you to get it flat against the sills if you angle your gooseneck down and give a good scrub, can also put some pink stuff paste or upvc cream on the pad if it’s really bad.

Just normally wash down upper ledges with the brush unless a customer requests more. (I've only had a few requests to clean them more than a brush and flowing water will accomplish in ten years.) When requested I've used Bar Keepers Friend on my brush to quite good effect on those grey upstairs ledges.

Thanks for the replies. To Moor I'll look at gardiners doodle bug pad holder and pad and  to Marko067 I'll have a look at Bar Keepers Friend. To be honest I only ever use the brush and pure, if its really bad spray a bit of virosol on the brush. But a few of the first cleans recently have been pretty bad, just trying to give myself options. It was probably only me that wasn't so happy trying to get every thing like new!