Looking for a haynes workshop manual for an 02 plate citroen picasso diesel here is the list of what needs fixing

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Squeel from somewhere on the engine (thinking maybe idler pulley)
Front Crankshaft seal spewing oil
Someghing much bigger causing the car to be painfully slow struggles to stay at 70

Squeal try spraying wd40 on to each pulley in turn which will quieten the one in question. Most likely to be the water pump at that mileage.

I'd check the engine breather first before the pulley seal, chances are it's blocked with gunk and forcing oil out past the seal which is not a high pressure type.

Going by what you've previously said about this engine it's most likely to be needing a good oil flush and an oil change plus new filters. Change out the coolant too and check the thermostat is closing fully and the engine temperature is reaching halfway up the gauge quicky as the thermostats are notorious for breaking and keeping the engine too cold. The plastic induction pipes are also known to crack and even split. Hope you have more room to work on the engine than my car which is dreadful.