Replacement spark plugs for the Iltis?

[Pedro Bedard]

I was told that Bosch plugs # WR7DC could make good replacements for the Iltis plugs.
Now, I found a conversion table that states that NGK plugs # BOR6ES are a suitable substitute for the Bosch ones.
Does anyone have any experience with either type of spark plug as replacement for the ones in the Iltis?
The Iltis runs for a while but when left to idle for a few minutes it just stops and won't re-start until the plugs are cleaned. Then it starts and does the same thing.
The guy who's doing the repairs on my Iltis says it looks like there may have been diesel or some other oil in the fuel. Might a drain-and-clean be the best solution? Or are, as he says, new plugs needed?
I appreciate any and all suggestions and comments.
Pedro