The problem you mentioned is very common. That is why AE made the change on the 12L4. The left side hub on the 12L4 is a standard IRS part. It is the best solution. It would be a good idea to re-install the metal stud in the end of the axle. It is very easy to do with thick CA adhesive. But since you probably will not be able to properly center the stud, the IRS hub would be the only way to properly hold the left side wheel. Good luck.