Several years ago I replaced my 1989 Oildyne hydraulic pump because, well just because it seemed ill.

 

Many people have had problems with their pump and its functions - often by complaining that the spool (shuttle) valve was in backwards.  Someone even sent a picture with the components laid out:

 

 

So, today I disassembled the old pump just for giggles.  Note that there is a number, 829, stamped into the frame:

 

 

Also note that everything is symmetric - there is no way to install the shuttle valve backwards.  There are some off center channels machined into the pump body.  Well, why did it fail to perform for me?

 

 

See the o-ring on the right check valve - it is damaged severely.  Right click on the picture and zoom in.

 

Before I start going after cylinders next time I have a hydraulic problem, maybe I'll just pull the valves here and check the o-rings.  I have no idea what my newer pump looks like inside except that it probably matches the first picture.