Depending on your mechanical skills and experience, the 560SL is a vehicle that you can do a decent amount of maintenance yourself. Spark plugs are straightforward. Take care in removing the boots off the plugs, then standard tools. They need changing at 30K because they are not platinum, use standard Bosch per the specs. As far as fluid changes, the recommended ones are motor oil, coolant, brake fluid, power steering and transmission fluid. The rear differential is also a candidate. Doing searchs on this forum will supply lots of good information.

Motor oil is easy, the drain plug takes an odd metric hex wrench, but you can get on the collar of the plug with a pipe wrench. The oil filter is a refill type, and is readily available...a bit different to change than the standard spin-on. Coolant is straightforward, drain for radiator is accessable. Use the correct coolant, Zerex G-05 is the right stuff (yellow, not Dexcool), or from MB dealer. Brake fluid is Dot 4, search articles on flushing/bleeding.
Power steering uses standard fluid or MB fluid. Transmission uses Dextron III. As far as filters, the easy ones are the air filter, oil filter, and power steering pump filter (yup, it's in the reservoir). The fuel filter(s) are in the rear underside and are a bit more of a job (maybe leave these to a M/B mechanic). The transmission filter is not bad, assuming you have done them before on other auto trans cars, somewhat messy, and requires removal of the transmission pan. I left the fuel filter and transmission fluid/filter change for a good independant mechanic (who works on Mercedes and other european cars) . Also check your brake pads and front suspension bushings. Good Luck