I've been working on a circuit which would drive an industry standard pneumatic regulator (E/P transducer).  The transducer takes a standard 0-10V command signal with a typical input impedance of 6.5 kOhms.  The DAC that I've selected (ADI 12bit 8 channel) has an internal 2.5V reference and can output 0-5V.  

After researching extensively, an opamp voltage doubler seemed like a good fit.  This worked and was rock solid for about two weeks, but failed after a ~2 day period of continuous operation without warning.  Now the opamp output is close to a correct 2.0 gain but constantly fluctuates as if the output is barely stable and poorly damped.  Has anyone ever seen an opamp fail this way?  

We're using a UA7812 linear regulator to supply 12V (from 24V) to the opamp quad (LM324AN) and admittedly it may not be sufficiently heatsinked (gets wicked hot to touch). Still, the 12V supply is solid at 11.83V and voltages supplied by the DAC appear correct and stable.  The actual resistors on the board are 10k with 0.1% accuracy and each measure 9.95k precisely.  Any advice in solving the problem is tremendously appreciated!  It's essential that this be a robust circuit.

Below is our final opamp configuration (and the part number):




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