Highest 13 keys on top and on bottom boards do not function

I would take the pedal board apart, repair any damage and put it back together again.

https://www.organforum.com/forums/showthread.php?50109-Wanted-Wurlitzer-Omni-6000-Keyboard-Computer
https://www.instructables.com/id/Repairing-an-Electronic-Organ/
http://www.casiomusicforums.com/index.php?/topic/13338-wurlitzer-organ/
http://forums.musicplayer.com/ubbthreads.php/topics/2332520/all/SK_1_and_2_Tips_Tricks_and_Oth

Try these sites

http://manualswarehouse.com/ofrm.htm

Wurlizer omni 4000 schematic

https://www.vintagevibe.com/pages/search-results?q=wurlitzer+omni+4000+schematic

You can find a tech in your area on this site-p

Electronic Repair Services for the Entire Music Industry MITA International

Since the organ has not been used for a long time, I suspect that there can be degradation of the electronics, specially with electrolytic capacitors. hence I request you to switch on the Organ continuously and allow it to warm up, it there is improvement , then it will be worth to remove the bottom panel and clean up the boards,dry the PCB with a hair dryer and reconnect the boards.
Hope this will help.

Your best bet is to contact Mark Morelock at-
Morelock Organ Parts MITA International

Hey, I had the same problem. You just have to off the Keyboard (by pressing the standby/on button).

Now hold the last key / highest key.
Keep holding it
And
On the keyboard while holding it.

Problem will be solved.

I haven't actually got the means to trace out diagrams on this particular model but I did find you a service manual if you have the technical skills to fix it.
https://celedoniaorgan.netfirms.com/cos2/index.php?main_page=index&manufacturers_id=19

Try voice 9 in the bank 96. That is for a theater organ type sound. You would need decent sound system to amplify this and to sound anywhere near decent.

If this is the kind of organ with the wire sticking out of the key that makes contact with the bus bar to create the note you will have to make sure that key is operating the same as adjacent keys. The busbars have to be clean and the contact wires have to be clean. Sometimes when cleaning the wires they will spring out of place and not make contact with the appropriate bus bars. Check that key against the rest and see what you find. Hope this helps.