My mother was born in Marylebone and always pronounced it ''Marry-le-bone'' and I don't believe she so much as visited anywhere in the Midlands in her life.
Could be a class thing, may I suggest.
For me, it's always been pronounced Marralabone.
Ewell -- pronounced 'Yool' -- is a puzzle for many people; just the other week on the bus someone asked me how to get to 'Eee-well'.
Some years back I did a phonetic map of London for my PhD supervisor's Russian girlfriend, as her English was at that point somewhat rudimentary and she had trouble matching the spelling and pronunciation of quite a few names. So we had such things as Tah'ill, Arra, Sahf Arra, Ern'ill, Ba'sea and many more.
Back in the days of spoken station announcements, nearly everyone at Hammersmith station, and there was quite an array of different accents, would insert an additional 'i' in two stations, thus making them 'Westminister' and 'Upminister'.