I own a Doerner desk chair. The only ID I can find is RD67. I use this chair every day but it seems the back leans further and further back each time I lean back.I have tried looking up the patent illustrations to figure out how to adjust but it seems most of the ones I found have the tension spring running parallel to the seat. Mine runs vertically. I have probably had the chair for over 20 years so I can't find the owners manual. Anybody know ?