Dried out felts can leak badly. Sometimes they recover a bit. Front can be changed without much problem but the rear one will obviously require the box, flywheel etc to come off to change it. Nothing wrong with felt especially if the surfaces that they bear on have got a bit rough with dirty oil. Lip seals don't work well on that sort of surface. Unless overfilled, oil shouldn't run out when parked, as the level is normally below the crank line. Lots of leaked oil may mean a badly fitted filter if you've recently done a change. Not noticing that the old filter seal has been left in the block can cause this. Clean out your side vent and the oil filer cap. If you've set up a PCV system with a few hoses make sure they aren't causing the block to be pressurised.
The sealing (freeze type) plug at the back of the cam can rust and allow oil to leak out but not very common.