My experience with used 732s: In the last five years we have purchased 4 732As and 2 732Bs. 2 of the 732As had unacceptable drift (3ppm/wk or more). The other 2 were nice units, with drift far below the spec of 0.6ppm/mo.
One of the 732Bs was bad, but it was the power board, so replacement was a snap. Both 732Bs drift about 0.1ppm/90 days, currently.
The problem is when you buy the first standard used. You have no way to check it. So, you really have to take it to a lab and have them check it.