I've read twice here that fuel in the plug of the SOV means the internals of the unit are leaking. Is this repairable or definitely need a new one?

This is an old leaky spot that wasn't high on the list. I'mm guessing it got worse because the DVs 1-2 are not leaking any more.

Time to buy a new SOV?

Yep definitely get a new one. Don’t forget the o-ring on the stem going into the IP it is not included with the valve.

Had to do this last summer it cost about $100 at the dealer.

Be prepared to renew the fuel lines or at least the o-rings going into the SOV, the car now has an air leak that I need to rectify when my son comes home for Christmas.

__________________
The OM 642/722.9 powered family
Still going strong
2014 ML350 Bluetec (wife's DD)
2013 E350 Bluetec (my DD)

both my kids cars went to junkyard in 2023
2008 ML320 CDI (Older son’s DD) fatal transmission failure, water soaked/fried rear SAM, numerous other issues, just too far gone to save (165k miles)
2008 E320 Bluetec (Younger son's DD) injector failed open and diluted oil with diesel, spun main bearings (240k miles)

1998 E300DT sold to TimFreeh
1987 300TD sold to vstech