So far I always used a certain type of NOS paper in oil caps in the 10Y line stage. Since my stock of these capacitors is dwindling, the 10Y line preamp got a slight update with new capacitors.
The oval cans got replaced by round MP foil in oil types.
All the rest remains the same.
Listening tests with the first line stage with the new caps proved that fears of a negative impact on the sound were unjustified.
So this concept can live on.