Check the "Cylinder Address and Difference"
board. Most likely it is
faulty.
BTW: Repairing RK05 is usually real fun and not much frustration :-)
How did you clean the head? Usually, with enough
patience (can be half
an hour or more), you'll get them clean anyway.
I use a match (the *wooden*
side!!!) or similar in conjunction with ipa
to get the crusts off. In the end I use some tissue with IPA to clean
the heads.
1. How hard is
it to mount the head in the tongue? Looks like just 2
screws.
I'd say practically impossible. At least I've never heard of someone
doing this in the field.
The official spare head is in fact a complete head assembly.