I think my 53 147 has the same problem. Without much warning I heard a vague squeaking and not long after I struggled to get it in any gear other than 3rd! Managed to coax it about a mile (was only a few mins from home!) before dumping it. AA came to get it and had to winch it on as you can't reverse in 3rd
Pretty sure my dealer said it's the linkages. They wanted £300+ to fix it.