I was nasds certified in 1973. My dive instructor was howard hall (www.howardhall.com)
I bought my Benthos 500 new in 1973 and it never worked right. I sent it back 3 times under warranty to get fixed. It's only problem was (and still is) that the second hand hangs on the minute hand after a few revolutions around the dial. Seems to me a simple fix. But as I said, everytime I sent it in it came back "fixed" then promptly stopped yet again.
I might be interested in getting this fixed once and for all if someone knows a reputable repair service, or maybe even selling it...