Having guarantee issues with KR Audio?

I want to add my story. .I have a cary sli80 amplifier and picked some kr kt88 tubes up for a good deal one of them failed after only 5 hours of use..I have 2 spares so I replaced the bad tube but I'm having a difficult time keeping the bias set..they seem to have wild swings. Not feeling confident they are going to last long. To bad because they do sound amazing. 

I am a longterm (>10years) happy owner of Audion 845 monoblocks and, after about a year of searching for optimal floor standing speakers for my listening room and amps, I ended up with Coincident Super Eclipses - with which I also have been extremely happy.
Some years ago I experimented (with some ignorance) with some KR845s and had early problems with tube flashover and blown components before I had the amps modified - took a couple of goes - to optimise them for the KR tubes, which were a superb improvement over the Billington audio ones they were supplied with - particularly in the bass. I have lived with the same tubes all this time and am still delighted with the sound of the system (BAT VK40SE preamp used not exactly as intended - into SET power amps) but now face a dilemma since I don't have a spare pair of KR845s. Do I try and source new (or NOS) KR845s, with all the bad stories about tube failure and guarantees not being honoured, or should I have the amps returned to original spec and replace the tubes with something like the PSVANE option?
Interested to hear from anyone on this but particularly 213Cobra and Beanie

I have a five month old pair of KR T-100 tubes in my Vinnie Rossi LIO DHT. I’m getting noise from one tube. There is a month left on the six month warranty. I emailed BEST300B.com and have not heard from them yet. Has anyone else had reliability issues with the T-100?

I'm far less than impressed by BEST300B.com and Franciszek Fikus (aka Frank.  I purchased a pair of " 300B Riccardo Kron Limited Series" (July 2020) and they shipped without the normal test certificates, stating tube measurements. When I complained, Frank said, quote "I am always at your disposal", and sent me a PDF containing test certificates, unfortunately not for the two tubes I had purchased (each tube is individually numbered). He seems to believe that "close enough is good enough". When I emailed him again about this problem, I never heard back from him, despite a second follow up email.
I emailed Eunice Kron to see if the factory kept records (easy in this say an age) only to be told no.
So a sour experience for tubes costing US$1,250 from the very get go.