I suspect you really had only one problem.There is likely a solid chance the old alternator is still good. Cheap or free recovery of it if possible to have as a spare might be considered.

Especially if the replacement alternator was a Mexican type of rebuilt. Basically there is no way the normal charging system can keep up with the presence of a constant glow plug cycle drain.

Thirteen point five volts is acceptable. The battery may even last longer than being forced or overcharged up to fourteen point five volts. A fully charged battery is slightly less than thirteen volts. Constant overcharge cannot be all that good for them over time. higher cutoff voltage only allows faster replacement of lost charge if required. There may be a cost for this though.

I have to wonder if it may be one of the reasons that batteries in service today sometimes may not last as long as they did when I was younger. Our old diesels once started in the morning have no load on the electrical system other than the radio on most days. I suspect the lower cut off voltage of our alternators may have been a design consideration.