My '87 300d (603) also puts out blue smoke at startup. I recently replaced GP's and cleaned the interior of the intake manifold and crossover pipe. This eliminated the blue cloud for awhile, but it returned once the manifold got oily again. Reading old threads on this topic seems to point to turbo lubrication leaks or valve stem blowby as the source of the oiliness. Am not sure how to isolate the source.