I have done a lot of research on AC problems and issues with the 300E recently. The consensus seem to be that the refrigeration efficiency of R12 is better than R134A, everything else being equal. The Nippondenso compressors used in your vehicle have pistons coated with Teflon and during failure, the resulting mixture of burned oil & Teflon can form a coating throughout the system. Another problem you may expenience is the 300E is prone to leaks in the evaporator. This is a very expensive repair. The question of coversion to R134a depends upon the nature of your repair (how extensive) and one of personal preference. I personally prefer to stay with R12 for as long as possible.
<LI> 1988 300E Metallic Blue Black/light Gray MB-Tex leather interior
<LI> MBCA Member