ARC Ref 3 preamp - updates or concerns

I am considering a used Ref 3. Are there any updates in its lifecycle or potential issues to look out for on these units? I will be pairing with a Ref 110 and also considering a new LS27, though the Ref 3 can be had for about $1k less than new LS27. Any feedback or advice is much appreciated.
The Ref3 is an incredible preamp. No issues here. It has been a stellar performer. I have no experience with the LS27.
Any idea on an average total life/hour expectancy on a tube preamp of this caliber? I would plan to fully retube it as soon as I receive it, but wondering what is realistic for total useful lifespan. My dealer was not certain of This units build date or the tube hours currently on it, as he just took it in on trade. Waiting for him to get back to me tomorrow with more details... I am wondering at what point does the value begin to decline in terms of total hours used. They are asking around $5900 for it.
The preamp will last longer than you will. Audio Research preamps last forever. There is an Audio Research SP-10 preamp currently for sale on Audiogon for $3600. It came out 30 years ago for $3700. It is selling for more than 97% of its original purchase price 30 years ago.
Your best bet is to contact ARC with the serial number and ask them if there were any updates made after it's production.

From what I've read there were some changes made over it's production run.
Post removed 
I had A problem with my Ref3, it wasn't a big deal, one of the tube socket's had to be changed at the two year mark, ( purchased it new ) , the repair was done locally. The hour meter can be reset, so be careful if your looking for a used one.