You lack to mention what kind of x5 you have. Is it a 6 cylinder petrol or diesel? is it a v8? A blocked pcv will cause oil leaks to occur, not so common in your earlier stuff though, but still possible.
The 6 cylinder petrol have a cyclone canister under the intake manifold, accessible behind the throttle valve. The 6 cylinder diesels is on the rocker cover and removal of several covers required, simple bolt off bolt on "oil separator", should be done every 3rd oil service and v8 should at the back of the intake manifold, underneath the cover with rocker cover hose leading to it.
Burning smell is probably a leaking rocker cover gasket, common between both the 6 and 8 as the heads are tilted over the headers.
Generally "blocked pcv causing oil leaks" are much more common in your BMW new generation 4 cylinders, X5 just leak due to age and deterioration. Also can be a pain to replace on the V8, other things that leak are power steering hoses, timing chain cover gaskets and nearly every coolant component.