The U.K. Selva web site is www.selvamarine.co.uk
.. you can order spares etc via this site.
Yes if the motor has stood for a long period the crankcase seals may need replacement.
However, before replacing the crankcase seals, try fitting new diaphrams and gaskets in the fuel pumps. If this fail to improve matters then ii's probably the seals.
If you send me a private message with your postal address I will send leaflets covering setting up the carburation on this model which should help your Dealer.