27 is an odd value, so I am going for the theory that they got a bunch cheap. If they are now faulty, that could also be a related reason. Put back 10 uf, make sure they are 105 degree caps.
If you don't mind I'd have to slightly disagree - we used the values we did because in those days they were the biggest values we could physically fit in, but these days you can fit larger values. If we'd had todays caps available the low end would have been much better! If I was recapping a 4k (not that I'd have the patience to do it these days

) I'd probably be at least doubling quite a few of the coupling capacitor values.
However I say "slightly" disagree because absolutely if in doubt fit the original value.
And totally agree fit 105 degree ones...
Cheers,
Andy