So 18 months to a year ago the Golf in the hands of Alex the last owner had a loss of oil pressure and needed the bottom end rebuilding. The culprit:

I've been suffering less than perfect pressure myself so today I pulled the pump out.

Look familiar? Seems to be paint and sealant on both occasions!
Oil pressure is now a healthy 20psi (1.37 bar)at idle @ 80deg Oil temp, hurrah!
Not the hardest job in the world but not helped by a paper gasket having been used last time the sump was refitted. It was a right pig to clean it all up.

I'll be cleaning up the old pump and adding it to my increasingly large box of spare parts. I spoke to Alex earlier and he confirmed it had had a new pump when the lump was rebuilt last time.
Nick