Unfortunately, we had the same problem on our Series II after a 5-week tour of Spain/Portugal, when we reached the South of France the bracket on the drivers-side completely sheered off. The Morgan repair garage was unable to help and eventually after a visit to Mr Bricolage for 'spares' we were able to bodge a repair that got us back to the UK.
When the car went to MMC for serice, they altered the brackets for something more substantial and we had no further problems; nor has AsboJohn had any, to the best of my knowledge.
I'm surprised to hear that you have had problems with a Series IV, as I thought that the problem had been sorted; though I did hear of other Series II with failures, usually it seems prompted by poor road surfaces.
Hope you get it sorted Scottie.
Aeroman
