gearbox for vanagon

[bretagne]

put this in the wrong section yesterday. hope someone has some some knowledge of this......
i have had some trouble for a while with my 1.6TD vanagon (1990, westfalia conversion). it has a replacement engine (golf) and 200,000km on the clock. a bit lacking in power but that i think is normal cos it weighs 2 tonnes, and the engine is always very thirsty for oil.
the problem though is the gearbox. it was rebuilt a year ago after a complete leakage of oil pretty much melted everything inside, but continues to leak, sometimes in drips, one other time quite substantially. it has become very noisy whilst driving and gets very hot.
is there a 'usual' place that oil tends to leak from?
where can i find the ventilation on the gearbox, as i thought this may be blocked up, hence the heat?
is the noise a sign that it is just too tired and needs to be replaced? i am hoping not, obviously.