The VHS mono audio was in a better quality than expected (though far from hifi). However, there are several serious asynchronization on the track. Also, it has some audio dropouts which are most notable during narration (pieces of audio are just missing).
After some tweaking, I seem to have found the parameters for dynamic compression and equalization in order to fill those things with a fold-down of the German BluRay dub so that the difference in quality is not very notable.
Here is an example.