The 48 is considered a magnum by most people, it should be doing closer to 20 fpe. Diana rifles are notorious for shipping bone dry from the factory, and shooting them that way for long can do some damage. You'll need to open her up to lube it, and YES, you do need a spring compressor. Doesn't need to be fancy or expensive, here's what I use:
Takes a little finesse, but this has taken apart lots of springers, including a Diana 350. It's a standard Pony pipe clamp, I think they're around $15 at any Big Box store. The screw is a little short for the long stoke guns, but it still takes enough of the pressure off that you can finish removing the spring by hand.
Might as well have parts on hand before taking it apart, at the minimum, you'll need a new piston seal, lubes, and perhaps a tune kit. I've used both Macarri and Vortek kits, and I like both. Price is about the same either way, total will be around $100. Or you can send it out for a tune, depending on who you pick and what you want done, that can run from around $100 to as much as you want to spend. Good luck.
Dave
