One of the problems with R-134 systems is the oil does not blend with the refrigerant. Another issue with the oil being used in the system, it is "Agroscopic" meaning moisture will mix with it thereby effecting the oils ability to reduce friction over time. Another factor could be if your system had a leak prior to this failure, and the oil in the system was not replenished to its proper level.
I suspect the life expectancy of the compressors on the transition systems (1996-1999) will be lower than those of late.
I have been hearing some good things about a synthetic oil called Ice-32. You may want to research it.