Reduced voltage to starter

[A65Thor]

My 2000 Merc 40ELPTO (2 stroke) suddenly won’t start. Starter spins very slowly, just growling and not fast enough to engage the motor. A multitester shows that there is 12 volts to the engine, but when the key is engaged, there is only about 6 volts to the starter. Can’t find any loose connections or grounds. Battery is fully charged. Any ideas would be appreciated. Thanks.