Capacitors for HP filters in tube amps recommendations?

I just prefer not to give myself a reason to think about possible timing/phase anomalies, anywhere in my music's path.      That's been my stance, since the early Eighties.       Like everything else; opinions vary.       

By the way, I too have bought parts from Michael Percy, the last time earlier this year. I hope he's doing okay, he's a great source.

Absolutely and good to hear, he's still in the game!    I always enjoyed our conversations, appreciated his ear and wisdom.

He's been in the biz a long time; I've been patronizing him since he was in Northern California. His online catalog reflects a wealth of knowledge and experience.

I said, "personally".       You’re welcome to your opinion, if you have one regarding time-constants (which is to what I referred, but- you never addressed) and anyone else’s, that you value.

I was trying to be helpful, not make anyone wrong... I'm sorry if it didn't come across like that.

The time constant of an RC filter is the cutoff frequency, this is set by the product of the total resistance and total capacitance in the network. So the accuracy of those two values will determine how close you are likely to get to what you're aiming for. Low tolerance components (e.g 5%+) mean there's a larger margin of error in relation to the target cutoff point - sometimes that's important (e.g. RIAA filter), sometimes not so much (DC blocking filter).
Components can also change their value due to temperature changes, ageing and other factors. So when setting the time constant it's most important to select components with the required tolerance and stability which is mostly down to the dielectric (PP, polystyrene, polyester etc.) and the quality of manufacture.  Using caps in parallel doesn't affect any of these qualities providing they've got a good electrical connection.