had the same problem on my 82 300TD. turned out to be plugged fender drains. Check the "pocket where the hinge rests when the hood is down, then below the battery and the brake booster is where the lower drains are located. A jet nozzle on the hose directed in these areas will do the trick. In the future, keep these areas cleaned of debris utilizing a shop vac.
Hope this helps, Rory Morrison Oroville, WA 1985 300SD 1982 300TD
