This may be okay, but it would worry me to death. I have been told that many times, particular combinations of oil additives don't work good together.
The ideal would be if you had a source of synthetic oil with no additives. Then by using universal oil like the truckers use, which have increased amounts of cleaning agents, you may be able to accomplish a positive without worrying about the negatives.
'84 Euro 240D, 523K miles
'88 300E 5 Speed
'81 300D Daughter's Car
Over 800,000 miles in