HP 33E Repair Advice

[kusmi]

I just acquired an nice looking HP 33E. It was sold "for parts" because the display had some troubles (segments not lighting up).

After some light twisting of the case (I guess this is the solderless version) - I got all LED components lighting up again, so the LED module seems to be working. Keys are working fine and it seems fully functional (RUN and PRGM mode). The battery door is broken a bit, but still closes.

But I have two problems and would like to seek some advice - before I try to open this little puppy.

1. Whenever a digit is shown, the top-most and top-right segment is always "ON", so all 1s appear as 7s, etc (see attached images, the first shows the display when I enter 1111111111, the second shows the number -1234567890). Those additional two segments are only ON when the actual digit is displayed - if the digit is OFF, all segments are OFF.
2. I see some greenish stuff on the battery contacts - I guess this is copper hydroxide. It is not much, but I don't know if the former owner has just briefly removed some of it (so there could be more inside).
   

What do you think regarding 1.) is this something which could be repaired by just opening the calculator and cleaning some contacts or does this look like a IC/circuit problem?

And regarding 2.) what is your recommended method to remove copper hydroxide? Just brush it off or are there some recommended chemicals? I guess for the battery compartment I could clean it more aggressively than on the circuit board...