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The problem with letters on the daisywheel might be that the hammer is either missing (some models have removable or replaceable hammers) or is present but disabled or 'broken' / in need of replacement.
As for the RETURN key not working... that could be anything. I'm not sure what it is in this case as yet. More info on the internal condition of the typewriter would be needed, as well as whether it is 'sane' in general... if assorted other problems with operation are present, it might have defective control circuitry.