How can you tell, visulally, a worn rec/play head?

[Seeker of Rock]

Or may from the capstan? Just wondering if you can tell by looking if a reel machine has excessive wear and what to look for?

 

[Beck]

You will hear it first. When you get it check all the tracks for function and equal playback levels. Record a steady tone (one track at a time) with a keyboard or tone generator at 0 VU on the meters. Play all 16 back at once to compare. One or both edge tracks (1 and 16) will often be low and/or fluctuating by several dB if the heads are worn badly.

Check the following link for a crash course on heads:

http://www.jrfmagnetics.com/headtrip.html

-Tim