Dave –
UMERC has also experienced quite a few broken ignition coil springs. UMERC has an open warranty claim with Wartsila for this issue. Wartsila did provide a failure report with multiple potential causes for breaking springs, and they are currently working to identify the cause.
As far as boot grease – UMERC received a thumbs up from Wartsila TS to use di-electric grease on the spark plug boot; however recently Wartsila rescinded that recommendation and told us not to use di-electric grease on the boot, because the grease collects dust/debris that can cause arcing.