I also have this engine in my Parker and have experienced this problem first hand. Infact its thanks to this forum that I spotted the siezed waste gate, which resulted in having to replace the turbo. Every now and then I get my brother to put his hand round the back of the engine on the push rod attached to the waste gate whilst I throttle up just to check its moving free and easy. This is obviously not a good idea when the engine is hot or in a lumpy sea. The best way to make to stay on top of it is to fit a boost gauge - I just haven't gotten round to it yet
. One of the machanics at Mercruiser recommended spraying fogging oil in to the aircleaner at the end of the season which should lubricate the wastegate. You can't really lubricate from the outside because of the fire blanket which covers it all.
Apart from this, its been a great engine (touch wood) and I've heard of these engines doing 4000 hours +. I think the early ones with the faulty spray pattern gave them a slighly bad rep. They just need a bit of TLC