Replacing Mica caps with film or ceramic?

[Jon1967us]

I have a number of Mica capacitors in sets that I am working on that are out of tolerance and a bit leaky. Since Mica caps are very expensive does it really make sense to go through the expenditure and try to source equivalent values and voltage ratings which can be upwards of 8 to $15 a piece, or with today’s manufacturing quality why not just use a film capacitor of the same value and rating?

I know that Mica caps present the highest level of stability, but honestly is this so critical in a tube set?

Has anyone simply swapped out a Mica cap for a film or ceramic?