My experience with my 2343 diesels is fine the rollers do not spark on the other hand my prewar 251E and 253 electric sparked a lot and would spark quite a but and become extremly hot just after a few minutes of running .
What i did was slightly bend the copper strip pickup assembly so the rollers would not right so downward on the middle rail to my suprise the sparking went away and after 45 minutes the rollers were not hot at all . Now it could have been in my case the roller assembly was bent down by someone in the past that i do not know but it is fixed.
On yours the only thing i can think of since you have tried most everything else that you may or may not have done is replace the brush well springs and try to have the rollers actually have "less" downward pressure on the rail just "slightly" less pressure to see if that makes a difference if possible with yours.
