Music Reference RM 9 Question

I am a novice, who has a friend/audiophile who has set me up with, or recommended my purchases for my system. I have gradually been building it to where it is over many years now.

I have owned the power amp the longest, a Music Reference RM 9, for over ten years. It was used when I purchased it. I use an CJ Premier 14 pre amp and a Wright SO4 Phono stage. I listen mainly to LP,s.

Recently one of the 8 power tubes failed on the MR9. I have read where it is best to purchase all 8 matching tubes but wonder the down side of just replacing the failed tube. I'm not cheap but pretty frugal, so I want to make a respectable choice, not necessarily buy just to have the best of the best. However I am OK with that choice , IF it is absolutely the only thing to do, given the circumstances.
Your best bet is to contact Roger directly or Sal at Audio Summa. They will give you the best advice IMO. You should also buy the tubes from Roger. He is one of the very few in this industry that knows how to properly match tubes. In addition, you might want to post this question over on the Music Reference forum on Audio Circle as well. There are some very helpful RM-9 owners over there.
Not to be a naysayer but....Roger will undoubtedly tell you to replace ALL your tubes! For 2 reasons, 1st - it's the correct answer IF you're looking for optimum performance but more obviously, 2nd - he's a businessman, of course he'd rather sell 8 tubes instead of one. If frugality is a concern, simply buy one (not what I'd do but...). If you do decide to just buy one, plz post your results. My guess is that, initially, it'll be fine, long term.....?
Hey can you clarify how old the tubes are? Reading your post it sounds like they could be ten or more years old. If that is the case definitely retube completely, it is way past time.
So....if all the tubes were installed at the same time, and you have exceeded the tube life based on what Roger says is the maximum hourly tube life of the output tubes in his amp, replace them all. Replace them all even if you are close to it. It does no good to replace a few at a time because you will loose track of the hours on your tubes. I like my customers to replace all the tubes at one time because if one goes, other might be on the verge of failing as well. Also, having all new tubes will sound a lot better than mixing new with old.