The front standard on my 'new' 5x7 is not square. I can see where someone put so much glue on the bottom of one side that it is not flush against the cross piece. Not being sure what type of glue was used, how can I can separate this piece?
I would think you're going to have to disassemble the front as much as is feasible, cut it loose, and reglue it. If you don't have good carpentry skills you might wish to sub the job out, but if you're handy and have a decent set of tools, a square, some levels, a clamp, etc you will be fine.
Mostenbockers Lift Off #2, http://www.homedepot.com/p/Motsenbo...ains-Tape-Remover-Lift-Off-2-407-01/100029845 , works well on most glues and is safe to use on all types of surfaces.
I do not know how well it will work on wood glue as I have never had the need. I did use it on a Burke and James commercial view to loosen the bellows from the rear standard frame. It did not soften the glue like it does with other types of glue but it did soften it up enough to separate the bellows from the wood frame with only surface splintering. You may have to keep the joint moist with the lift off for a day or two for it to work on the wood glue.
My second choice would be to use a thin blade knife and tap it into the seam on both sides and and gently pry them apart. Old wood glue becomes brittle with age and will chip off or separate from the piece. Once separated scrape the old glue off with a sharp wood chisel.
If your lucky, and it was made with hide glue, its repairable. If its any other glue, you may damage the wood trying to take it apart. Google hide glue & you should be able to find info on separating it. I would heat it up in the oven to about 155F & if it starts coming apart, its hide glue. Be sure to re-glue with hide glue.