It might be as simple as the stop button being a bit dusty and not making contact...

Back before cd writers had buffers I often had disks crap out on me at the end of writing, but soon learned the disks were sometimes ok but not 'closed' or 'finalised' - if you have a computer with dvd writing software, you may find you can put the disk in and finalise it using the computer dvd writer.

Not a perfect solution, but a workaround. Otherwise I guess it's the new machine.

They don't do rf in/out anymore? Your mode of operation (vcr to dvd recorder) would be better using component or at least composite connections, rather than rf since the path is thus:

Component video (assuming that's the internal native format) converted to rf (tv/radio signals) out of one machine, into the recorder's rf, convert back to component video. Lots of quality issues.