Diesel fuel in the oil

I recently bought an '87 300SDL with 150000 miles. It ran great for about 10000 miles. But now its gotten rough idling immediately after starting and I'm getting about 1 quart of diesel fuel in my oil after driving about 200 miles after an oil change. The oil level dash light comes on and the oil pressure drops slightly (to a little above 2). I've limped home and changed the oil and filter and it happened a second time. The MB service facility (not a dealer) changed the injectors but that didn't help the rough idle or the fuel in the oil. They now feel it might need a new diesel fuel injector pump (+$1500 rebuilt from MB + labor), but before I do that I want to feel sure it'll fix the problem. Can anyone tell me how the injector pump can release fuel directly into the oil? Is this common on this motor (603.960)? Is there any way to test the pump for this problem? Any other insight as to what else could be causing these problems?
Thanks, Heins