Refurbish a classic amp or replace it?

I have a Mark Levinson ML3 amplifier that is over 20 years old. It sounds great in my system and I am considering whether to have it refurbished/upgraded. I spoke to one place that only does service and upgrades and was told not to do it and that I should sell the ML3 and use the money (plus a lot more)to buy a new amp instead. If I buy a new amp, it would probably be a Pass Labs. I would like to hear from other members who have had similar experiences. Also, I would appreciate recommendations for where to have the ML3 refurbished/upgraded if I decide to go that route. Thanks