Do an oil change for sure. Should be pretty straight forward. It sounds like they are in dire need. Might want to go a bit farther than just removing the top caps to drain & refill. Each leg has a 15 or 14mm nut on the bottom, removing those will allow you to drop the lowers & clean them & also grease the bushings and seals.
Stock oil is Golden Spectro 125/150 (7.5) although any good moto suspension oil should work well. Many people have gone to 10w with great results. Slickoleum is what I use to grease the bushings & seals. Same thing as Slick Honey or RS Butter, but cheaper. I'd lightly grease the bushings & seals, the seals can get quite sticky if not greased although you'll have to wipe the stanchions a few times for the first few rides.
Hopefully you don't have the same issue I've had with a few Z3's where for an unknown reason even after a full service they remain super slow in the rebound dept regardless of rebound setting after a full rebuild. The Z3's & Z1 drop offs have a similar cartridge design if I remember correctly. I've never any rebound issues with many Z2's, a couple 44's & 55's & a Shiver though If slow rebound continues after fresh oil & grease, you might want to remove the cartridge and let it soak in a big ziplock bag of rubbing alcohol for a day to see if maybe it's sludge buildup.
Good Luck! Marz forks are pretty easy to service & rebuild especially after you have the 1st one under your belt
Oh, something to catch the oil in is pretty important, gloves are nice & have some ventilation. That old oil can be quite pungent.
