Bauer manual: A simple switchover from mineral oil to synthetic oil is only possible during the first 100 operating hours of a new compressor. Beforehand, the compressor has to be cleaned thoroughly. Older units have to be checked by a qualified service technician prior to the oil change. Synthetic oils tend to dissolve carbon deposits inside the compressor. The dissolved residue will clog filters, valves and coolers. A switchover from synthetic to mineral oils is possible anytime.
Of course you can switch but you must clean the compressor in every detail. Cooling coils are very hard to clean. As a Capitano only makes low rpm oil is not subjected to stress at all, mineral oil has been working fine for decades for this application. My Capitano has been running on mineral oil for 45 years now, no issues.