and don't forget that ,with the VW Beetle lights -
VW N/S is Morgan O/S and VW O/S is Morgan N/S - not confusing at all

I would also echo Alistair's advice re. over tightening; it is very easy to split the grey rubber/plastic seal if too much tension is applied.
I seem to recall that Nick had real difficulty in sourcing new replacements a year or so back;I don't know if the supply has improved.....
James
If you want genuine ones be prepared to spend 6 months searching far and wide... if you don't mind aftermarket alternatives they can be sourced easily enough last time I looked.
Most will require a bit of filing to fit flush against the wings, otherwise they can sit a bit proud in places.
Hopefully mine are ok when I eventually drive it, had to do them up tight to get a nice flush fitting!