oil consumption
If you do not seee any major outside leak (front of engine, right/rear of engine) do not look any further.
It,s valve seals/guide time
JackD
Normally the oil comsumption is a combination of burning oil due to valve stem/guide problems, worn piston rings and leaking on the front end. If only the stem seals are the problem the repair is quite reasonably priced. If the front end needs to be overhauled bigger $$$, if the piston rings need overhaul there is a lot more to do since the top of the engine is open => $$$$$.
If you loose 1,5 liters per 1000 km you dont need an oilchange anymore :-) which saves you some money, only a new filter once in a while, may be not even this, since the oil disappears before it's getting dirty.
I had my valve seals replaced first at 120,000Km and the valve guides/seals replaces at 230,000km. Engine compression was still at original specification value at 230,000km with absolutely no sign of wear.
I would recommend to start with new valve stem seals (relatively cheap) and see the results.
JackD



