TUBE NOOB: ADVICE NEEDED ON REPLACEMENT TUBE

Recently my old man has given me his phono section. It is a Soundtech Preamp one, and no I am not expecting that anyone will know what this is. It is a tubed, pure class A, dual mono phono section with what looks like 2 independent power supplies, internal (strange). The unit is awesome, I think the retail cost was about $1800 in the 80s/early 90s, which does make it a little pricey for the time, but putting all price/performance issues aside I will say it is an amazing phono section. Now my concern is that I know very little about tube equipment and I am seeking some advice on finding a replacement tube for this piece. The tubes are quite old and I think I can achieve improvement sonically by replacing the old tubes.

The guide indicates that the amp uses 2 6CL8A tubes, a very unusual tube that I know nothing about despite my best research efforts.

Now, I don't know what to do. I have found some old tubes on ebay, but how do I know they will not be junk ? Maybe the unit can be modified to take a common tube? Is there maybe a way for me to find a tube equivalent, hopefuly with something that is still manufactured and intended for hifi audio use?

I am at a bit of a loss, so please give me some suggestions. I will post the schematics and guide manuals when I receive the electronic copy via email from the company. Also if anyone has used this amp, I am interested in chatting with you. Thanks guys.