The white GUNK is emulsified oil and water - the water comes from condensation within the engine and generally accumulates if the engine is not being run for long enough for the heat generated to burn off the water.
It generally won't do any harm but if the cause is short runs I would advise changing the oil a little more frequently.
Is the oil from the leak sitting on top of the joint between the gearbox and engine or is it dripping from it from below ?
I'm having a guess about the next bit - I've never owned a 97 corsa just a 94 and a 98 one- If it is the same as my 94 corsa and is fitted with a distributor - I would suspect the ' O ' ring on the distributor needs changing - if it is from below it could be the crankshaft oil seal at the gearbox end of it.
An inspection by a mechanic should be able to pinpoint where it is coming from.