bufflehead: Nice hand painting! That was a good way to go...very realistic. I like the drip near the weld seam.
You questioned the oil washes. I have had success with a build up of washes (you asked about my weathering techniques on the 251, remember?). Raw and Burnt Umber REALLY add a lot of depth and interest to the finish and I recommend going that route. They should be applied BEFORE the pin washes and should be a thin mixture. Experiment a bit, and don't worry if the coat is not evenly applied. Push the wash pools into areas prone to less wear...and when it's close to dry grab a 1/4" flat brush, moisten it slighty, and add some streaks with a downward stroke, especially below grab bars, weld seams etc.
Alternate raw and burnt umber...2-3 each, ending with the burnt umber, it looks great on a green background! If you have green oil paint and white (if you dare) add those too. The green will be applied with a tiny brush on the areas prone to sun exposure, specifically the horizontal surfaces and the top leading edge of sloped surfaces. Just add tiny dots like the dot technique...the difference is these are dlitued mixes, same as the other washes. Don't spread them too much just dab and let it dry. Do the same white the white but DO steak it when its near dry. Don't panic if the green and white seem BOLD at first, they tone down a lot during drying.
After all the washes are done, I suspect the stark white of your markings will be WAY muted, probably too much to your liking. To bring back the nice white, moisten a q-tip and rub off the washes..but be selective on where and how much you remove...too much removed will look strange.
Give it a try, let me know how it goes!
BTW: Is this the Tamiya kit? I've always liked this tank.