Engine mount off, cam belt covers off, cambelt off.... Replace oil seal. If it was me I'd be putting a new cambelt kit on (this envolves removing rocker cover) as well as the belt must have got oil on it if its leaking that badly...

Cam seals (mights as well do both) - £10
Cambelt kit - £80 ish....
Rocker cover gasket - £10

I'd expect a garage to charge you £250 for that lot to be done, so I hope your "mate" is doing at least that for £250..!!!

Take you time 4-5 hours... (a garage would take 2-3 hrs maximum)