That is good news that Bruntons will swap the zinc for the Red Cap in the bearing kit!
Let me tell you what I know and also what I believe about this issue.
- I know that if more than one zinc is connected to the bonding system, the zinc closest to where all of the bonding wires are bundled will deteriorate first. This is the reason that one zinc on the rudder usually goes before the other. When you place a zinc on the propellor, it will go first because it is the closest to the bonding system bundle and the closest to the major components of the bonding system.
- When that propellor zinc deteriorates, it does not uniformly deteriorate. This means it will cause a slight imbalance in the propellor shaft...probably, not noticeable.
- When the propellor zinc deteriorates it will be the three mounts (where the plastic bolts secure it to the prop) that will go before the larger part of the zinc...in the end, causing it to remain attached with 1 or 2 of the bolts before slung-off by the rotation of the prop.
The primary reason I prefer to use the Red Cap is because Amel says to do it. The other reasons become obvious after reading 1-3 above.
I hope this helps you.