Well, there are some component parts on the M79's that are not being made and haven't been for some time now...
The Vactrol Vactec, which is an opto-coupler, are impossible to find, as the company stopped production of these over ten years ago. They have a tiny lightbulb inside that WILL EVENTUALLY BURN OUT. The Vactec controls the record and erase circuit, so without it, you can't record or erase a track properly. You may end up with 16 of the 24 audio cards working, which you can move around as you track and overdub, since the playback will still be working... The only permanent solution to this problem is a mod that replaces the Vactec with a currently available and common component. The problem with that is, that noone (including John Klett, who is a huge proponent of these machines) has been able to come up with a mod that works because of the stringent requirements that ONLY the original part could fill (and there are no modern equivalents).
Also, there is a logic control chip (MC672) on all the audio cards and one or two on the logic cards that are almost impossible to find replacements for. The last time I checked (in 2001), no new MC672 chips were being made and all I could find was NOS components, sometimes of which you would have to buy several at very high prices just to get one working chip.
In my experience, having been engineer and resident tech in two studios that operated multiple M79's, as well as owning one for two years, Those two components are a major mode of failure for an audio channel on these machines, as on every machine I had to repair about 1/3 of the channels with these components being bad. Not only that, but they are maintenece hungry bitches in other respects, too... Now, since they are relatively easy to work on, it's not THAT big of a deal, but you will be working on it all of the time.
Aside from all of that, these machines are great sounding and very enjoyable to record on, though being slightly primitive compared to most decks in terms of autolocate functionality. There are some available aftermarket autolocators that will take care of that, and I've been able to get two of these machines to lock together (or with any timecode source) with amazing accuracy.
I'd say 2000 is a decent price for an M79 with a good set of heads, especially if you are willing to bear the cost of maintence and replacement of worn parts.
