That is horrific ! I take it you're favourite run is through a farmyard ?

Agreed, it isn't good and I do spend most of my time riding some terrific rural roads in all weathers, but not off road.
My point is that, certainly on the Mk 1, you can't keep your rad spotless unless you avoid wet roads and take the guards off every time you clean the bike.
The ideal would be to flush fresh dirt out from the back of the rad, but there just isn't room to get a hose or airline in there, because of the cooling fan. Also, the guards are all positioned too close to the radiator fins, so any dirt that gets through the mesh just stays trapped. The useless designer stubby mudguards don't help at all.
If the bike overheats because of a blocked radiator, you have a major problem, because the dirt will probably be baked in and won't be easy to shift. I have found condenser cleaner to be pretty effective, along with a lot of soaking and gentle brushing. Of course one mistake and buying a new rad could spoil the entire day.
I should add that my oil rad is now 100% clean and the water rad about 95% clear. To do the job right, the water rad would have to be removed completely, which I will do if I get overheating problems.
Of course a nice new Mk 2 would solve all my issues, but I'm still working on that.