The car: 1984 190D 5spd w/ 190k miles

The problem: Difficult cold starts manifested by 30 to 45 seconds of cranking, smoke, and embarrassment.

The question: What's the deal? The glow plug indicator lights as per usual--what exactly does the indicator light signify (ie power to the GP relay? Power to the GPs? Other?). The glow plugs themselves are less than two months old. Could this be a vacuum issue?