Washing stainless steel separator from organic residue
First try commercial cleaning solutions such as Alconox or Pierce RBS-35, with ultrasonic agitation (if you can sneak a transducer into the reactor). 

Second, an oxidizer such as Godax Labs' Nochromix might work, but test it on an unimportant part of the reactor to see if it safe and effective. Read and understand its safety data sheet before use.

A last choice is chromic acid, $\ce{H2CrO4}$, which in some concentrations does not damage some types of stainless steel.  N.B. Chromic acid is toxic, carcinogenic and harmful to the environment. With chlorides, it can produce toxic and volatile chromyl chloride. In high concentration it can cause ignition of materials. Check a material safety data sheet before trying it! Also prepare to dispose of this as hazardous waste.
Even if the reference states it is safe for the particular steel in use, try it on an unimportant area... perhaps with some of the organic "gunk", to see if the gunk is removed and the reactor is unharmed.