The most common, and easier to fix, hydraulic leaks are:
1. A hose that's loosened and needs to be re-tightened.
2. A hose that's leaking from its ferrule, which is the metal fitting swaged on to the hose. The hose will need to be replaced. HWH's part number will be on a white band near the ferrule. If it's unreadable, try taking a photo with a cell phone or digital camera. You may be able to read it by adjusting the contrast.
3. A ruptured hose, which will need to be replaced.
4. An overfilled fluid reservoir. This is self-limiting in that the excess will be purged as the slide is used. This is unlikely to be your problem since it doesn't sound like you've topped off your fluid. I suppose it's also possible that your fill plug has worked loose and may need tightening or may be leaking for some other reason, in which case replacement is in order.
There are many other possibilities, leaky cylinders, a leak somewhere on the control unit/pump, etc., but these are the simpler ones.
You can find HWH's system diagrams at the site below. This will help you ID all the parts and hose routings. For some reason, I couldn't find the 39K in the 2007 link but it does appear in the 2006 link. Note that there are two systems listed for the 39K, a 325 and a 625 so you'll need to figure out what you have.
https://www.hwhcorp.com/winnebago2017_diagrams.html
Note that some hoses will appear to be much too long and will be bundled up to control the excess length. Don't think they can be replaced by shorter hoses. They need to be that length in order for the fluid flows to be balanced between different parts of the system. IMHO it's best to order exact replacement hoses from HWH, they're not overly expensive and it takes about a week. I've read where many have had replacements made locally and you may save time and a little money but I prefer to use the HWH parts.
Replacing a hose isn't overly difficult but can be intimidating. I just replaced one yesterday. The most time consuming part can be removing the old hose and routing the new one since they're tied up in big bundles. Fortunately the one I replaced was one of the shorter and more directly routed ones.
My MH had several leaky hoses that I had replaced professionally but they either missed one or it started leaking recently. HWH had a problem with defective hoses in the early 2000s.