97/97 1.0L POLO OIL LEAKAGE- CAN NE1 OFFER ADVICE???

[c.l.w.design]

I have the above polo, it has recently been serviced at this point the oil was changed. For about 2 years there has been a slight oil leakage, I have had a mechanic check it and they couldn't find the source of the problem, I know its not the head gasket. I jet washed the engine and about 3-4months after this the oil came back, what could be the cause? The leakage seems to be on the bottom right-hand side of the engine.
Thanks