OIL THAT GUN, FELLA!
Remember, just because these guns aren't real, doesn't mean they don't need maintenance. Most of the time light Oil, BUT NOT WD-40, is all these guns need. Many of them however, should not ever be disassembled. It is very tempting to disassemble your gun to become more familiar with it. Try to restrain that urge, because replica guns are not built like real guns, and even the fella who is most familiar with REAL guns may not be familiar with the way a replica or blank gun is put together...Very similar, but not the same. Furthermore, disassembly voids all manufacturers' warranties. So......
Light Oil, and white lithium grease is a good way to go! All metal on metal parts work better together after a period of mutual wear, but too much wear can ruin a guns action. Light Oil and Lithium grease will help keep your replica weapon factory fresh for many many years.