ets checkout of a specific revision

Is there a way to use ets checkout to checkout a specific version number?

I think I have discovered a newly introduced bug (see my separate thread), 
and I would like to  see if I can figure out which version it was introduced in. 

Also, if this is possible, how would I use ets develop to develop the older
revision. 
Ets develop seems think I have the more recent version so I doesn't clear out 
the old version. How do I "remove" a newer version in favor of an old one?

thanks,
D