Technics have been putting serial numbers on their SL-1200 and SL-1210 turntables right from release in 1972 (1979 for the Mk2). This serial number contains the year of manufacture and in some formats the month as well. It will be a 10 or 11 character serial number consisting of both numbers and letters and is located on a sticker on either the bottom of the deck or the back. From 2008 onwards an actual full date is stamped on the tonearm base cover.
Technics serial number :
Click herefor an idea of what this Technics turntable may be worth
If this tool fails to return a result or you disagree with it please contact me. I will look into it, attempt to get you a date and then fix/improve this tool.