I'll give the red spring a go! The current spring certainly does seem pretty weak compared to other machines I've played.

As for multiball, I've had a good look, and it appears that the end of the wire (right side) on the left switch in Pirates Cove is getting caught on the upper side of the hole where it is positioned. The kicker must be vibrating or bumping the switch back into place, but for the several seconds that is down more than it should, it is probably what is preventing a second ball from being loaded into the shooter lane.
This may prove to be difficult to fix, as the plastic covering the Cove is not going anywhere and I'm not 100% sure how I would go about fixing this from under the playfield.

Thanks for all the support so far guys! Internet is a wonderful thing!

Cheers, Tom

PS: How does the postage work / how much is the postage on items from rtbb.com.au?