You shouldn't use DOT. Seals and hoses are not designed for it; however Mineral oil (Shimano, Clarks, Magura etc) is fine.
Magura Royal Blood (their brake fluid) is hygroscopic mineral oil (about 15 quid for 250ml).
Best thing to try first is to check the level in the reservoirs - make sure the levers are parallel to the handlebars & just pop the tops off the reservoirs to check the levels.
Often the older Julie (non-Julie HP) brakes just need topping up if for any reason the level is low. These were essentially a disc version of the hydraulic HSxx calipers so there's no need necessarily to completely bleed the brakes. Just top it up, put the seal and cap back on, tighten them up, pump the brakes a few times, then re-open and check the fluid level again, and top up again if necessary. If still no better, you might need a full bleed of the system & best then to use all-new fluid.
They're really good brakes to start on & work with - even a bit of trial & error usually won't damage anything provided you're using Mineral oil (preferably Magura's own) and you take care not to trap/damage the rubber seal over the reservoir.
The original Julies were made for a good few years; and Magura are one of those companies with a website like this:
http://old.magura.com/en/products/older ... loads.html 
