[Drake] R4B noise

[ed brooks]

My R4B is starting to sound a wee dab raspy.   So far I haven't opened 
the cover (if I had I would just trace out the wiring) but was browsing 
the schematic to see what filters are in the line.  Seems C90 is the can 
of suspicion.  But on the schematic I find C90B, C90C and C90D.  I have 
searched with these old eyes for C90A and can't find it. Guess I could 
get out the magnifying glass.  But section A may not even be used.  B, 
C, and D, are all 100 mf at 200 v.  If A is used, (and it may not be) 
can some one help me avoid eye strain and tell me in what circuit?!!  Or 
will I be relegated to pulling the covers and tracing the circuit?  And 
where can I find a suitable replacement can if it turns out that is what 
is needed?  (Surplus Sales didn't list any such animal under four 
section cans.) 
Thanks
Ed, W5HTW