New rings are very unlikely to fix a low compression problem as the cylinder walls are surely worn beyond specs, and you really need to de-glaze the cylinders to put new rings in anyway.

On top of that, new rings in oversized bores will quickly ruin the pistons. If you need an overhaul, do one, don't bother with "quick" fixes, they almost always end up being more trouble and expense than doing it correctly.

I would not attempt this in place, I really believe it will save considerable time and effort to pull the engine -- they come out pretty easy on those cars, you can even leave the hood on!

Peter

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1972 220D ?? miles
1988 300E 200,012
1987 300D Turbo killed 9/25/07, 275,000 miles
1985 Volvo 740 GLE Turobodiesel 218,000
1972 280 SE 4.5 165, 000 - It runs!