There are no easy answers to your questions. There could be PCBs in the transformer and also in the switch. A local utility might be able to refer you to a lab that does their oil testing.
Aside from the regulatory aspect, the oil should at minimum be tested for dielectric breakdown. There is a standardized tests and portable testers for this purpose, but if the process is unfamiliar, get an experienced firm to do it. If dielectric breaksdown is OK, [and it is pure mineral oil] then you can decide on an oil handling course.
