If you think you may have some irregularities in the mating surface of
the pump to block area, there is not one thing wrong with smearing some
HIGH TEMP silicone on that area.
One caution.
Be darn well sure that prior to filling up the cooling system and
letting her fly that you allow the stuff set up at least overnight.
(8 to 10 hours)
Then fill her up with coolant.
It'll never leak.
Forget the Deutschland no seal purist's.
They haven't figured out that it's the 21'st century yet.:-)