from your post i get that the DIY route is a no go for you.
The camera is a valuable one, so there are good reasons to give it to a competent technician, and have the fungus removed.
Please consider my advice: DON'T sell the camera as-is!
If you are honest, you'll loose plenty of money (on the other hand, if you ask too much it would go unsold).
Reading between the lines, i get the impression that you want to take the loss, and end it all as soon as possible.
Hurry is not your friend. Buying and selling is not the perfect solution for everything.
Generation of photographers have dealt with less-than-perfect cameras, and used the services of repairmen.
You don't have to find a "specialized" repairman, dismantling the back cell and removing the fungus isn't a very complicated task. Any repair shop should tackle the problem quite easily.
I don't live in the USA, and i am no Rolleiflex expert (i own a Tessar one since long time, but it didn't see much use), so i can't give you any practical information. Though i am sure that many forum members could reccomend a good Rolleiflex technician, and that finding one with good prices isn't impossible.
You could take two birds with one bullet, and have the camera overhauled.
After that, if you protect the camera from damage and store it in a cool and dry place, it would outlast you... and probably your children too
I would shoot a roll before sending the camera away: that way you'd know in advance if there is any need for a checkup, or just a simple cleaning of the glasses.
A Rolleiflex is very robust and very simple; if film advancing and shutter timings are OK, then i wouldn't spend any money for a checkup.
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