Officina Bugamelli ( info@officinabugamelli.it ) is the best place around here to have your engine overhauled/checked/improved etc. In December 2009 they grinded the valve seats and fitted new valve stem seals: the result is nothing short of admirable, the exhaust of my 409 being now completely free of any smoke. I am indebted for these splendid pictures to mr Bugamelli  himself.