Tube replacement on Aesthetix Rhea

I had replaced the tubes in my Rhea with Telefunken 12AX7s (V1-4) & Siemens 6922 for V5. The Telefunken on V4(R) was making noise so I swapped out both V4s (L & R) for the stock Sovtek 12AX7WBs. My question is: Do I need to replace the pair at V4 (R & L), or can I just replace the bad tube? My instinct tells me I should replace the pair so they perform more or less equally, but I remember someone saying in an older post that tube matching is not that critical in a preamp tube. I hate to trash a perfectly good Tele, but I do not have a tube tester. What say you?
Stew3859, Looking forward to what you glean from our members at A'gon. I too have a Aesthetix Rhea and looking at a tube roll even though by the most part I could not be happier. We'll see. Cheers!

I run with the Callisto and Io and for the longest time, I was not using matched pairs of 12ax7's or 6922's. The problem I have had with Tele 12ax7's is that none of the ones that have crossed my path work well (read: ultra low noise) on the first input stage of the Io.....all other stages this is not an issue. For now I use EI 12ax7's on this first stage until I find a pair of low-noise Tele's or Mullards to go here. The Sovteks are a bit fatiguing after hearing these other tubes.

Just recently I got a tube tester and was able to match pairs in terms of signal strength. I used all the higher tested tubes in the early stages but other than finding a couple tubes that measured weak and thus were replaced, the sound is all the same.....very lush! But there is no way for me to know the true outcome if I put in non-matching tubes. I guess I'll have to try this as I have the ability to match or mismatch accordingly. So I will have to do this and report back.