I decided to strip my Radiator to see how blocked it might be, I'm sure the last owners had added K-Seal and or Steel Seal into the water system.
Picture shows the reversed side of the top and bottom covers and the other picture shows the bottom of the radiator, just pushing a hacksaw blade into the chambers and red sludge started to come out. i did this to about 20 chambers and all was the same (This hasn't helped with my overheating)

Looks like you've had both in there. K-Seal leaves a residue of copper powder while Steel Seal leaves white stains on everything. Both claim to not clog things up but that isn't what I've found.

Good luck with resealing the rad, I've always thought that once apart they'll never go back together properly again so haven't even attempted it.

No Just going to get new one as only £70. Not worth the effort to repair, So one problem down several to go.

£70.00? That'll be Britpart then! <br>
Your choice entirely, but you can buy OEM quality for £115.00 ish. That way you probably won't be replacing it again in 6 months!