Through all the years I operated Liquid Ring compressors as both vacuum and compression devices, all I ever carried in stock were shaft seals. The machine is inherently maintenance free due to the use of the liquid piston and lack of any metal-to-metal contact with the exception of bearings and seals.
I never took a second look at the maintenance manuals. I never had to repair a unit. This doesn't mean you should shun inspections and yearly check-outs; you simply have a well-designed, simple machine. The maintenance requirements center around the support equipment: the fluid circulation system and instrumentation.