First of all, internal problems involving bearings and other metal surfaces will be found in an oil spectrometric analysis. Second, a spun bearing won't cause an oil increase in oil consumption. Third, nothing was said by the original poster to suggest a spun bearing. Fourth, not enough information is given. Fifth, we don't know the oil level the original poster is attempting to maintain when he keeps adding a liter. Sixth...oil pressure can easily be adjusted up.
Find the problem first, start small and simple, and work up from there. If you have doubts about the airplane, obviously don't fly it.