I have all three cars as you can see by my signature line. The 92 300D 2.5 is the best of them all in my opinion. Better handling...and almost as smooth a ride as the 300SDL but it is quieter and gets 8 mpg better than either the 300SD or the 300SDL. It has 210k miles and I have had no motor problems at all.
The only significant repair I have made to the car is replacement of the evaporator and that was a pretty tough 20 hour job (look it up here in the forum).
My only question is are you sure that it is an 87? The 87 300D's only came with the 6 cylinder 603 in the USA. 300Ds with the 2.5 602 were sold in the USA in 90,91,92 and 93

__________________
Tom Hughes
St. Louis
84 300SD
92 300D
86 300SDL