Thanks folks, closing in on completion now. Today I've been muckying up the exhausts and adding all manner of soot, grime and rust (only on the sheet metal bits). Rust was done with the excellent ak pigment the other streaks are also AK products. Finally I've found some proper late pattern resin hub caps for the sprockets.
Getting close to the end now, been adding the mud and weathering the tracks this afternoon. Now before anyone pull me up infront of a courts marshal for rusty tracks, they've come out way redder than they should of and I'll be making sure they match the mud on the rest of the tank.