Having only owned N/A MBz deisels, I can say that the N/A cars are very similar to the older 5 cyl turbo cars in terms of acceleration. The 98-99 will be much snappier.

Given the mileage of the older 124s and even 210's, you really ought consider a CDI 05-06. It may in fact give you a lower cost of ownership due to mileage. And they make the turbo 606s feel like slugs.

BTW, even though the motor lost a vacuum pump eventually ( due to low oil ), when I pulled the head off a '95 606 that had been run on B100 from 225-255K, we couldn't believe how clean everything was inside. BioDiesel is excellent stuff. Can't comment on WVO, as our feedstock comes from many chicken wing joints ( hence WINGAS) and I wouldn't run it without "brewing" it.

All the rubber O rings will eventually fail. So buy a complete Viton O ring set. ( does Jim still sell these??) The only PITA is the IP DV seals, as you have to be uber careful, like surgically careful doing that.