David Hafler 500 power amp..update worth it??

I've had this amp since 1986,with very little use.
It continues to get good reviews despite its age.
There are also several updates available that seem to add life to this old beast.
Is the updates worth it...are they as good as they say?
I'm thinking of selling and putting the cash towards a tube preamp.
Sell or update and use with my second system??
Are you taking about the Van Alstine mod?
Actually I don't know how many updates or recondition packages are available.
Which I guess leads to another question..which update is recommended.
I see a Omega Star update.How many others could there be?
The Omega is the Van Astine.
Here is another one. I have a XL600. Can't decide what to do ,sell it keep it......