Coupla a tips...
Nose plate
The Lexan nose plate is the weak link in the Makos. It can implode sometimes at quite a bit less than the rated depth. I peice of 3/16" AL plate can be cut to fit in this spot and sealed with silicon. I had Steve Gamble of
DPV Repair make mine for $25 I think. Cheap insurance.
O rings
I have made my own orings for my Mako using buna cord stock I got from Macmaster. I bought a kit with various sizes cause I was actually trying to get the main oring to be just a smidge larger (its was leaking on the stock oring). So I can't tell you the exact dimensions for the different rings. But you can measure the existing with calipers and get the same or 0.5mm more or less if you need to change the size. The cord stock glues togetehr easily with superglue.
Aftermarket batteries
For freshwater you want the Powersonic ps-12180. These are 18Ah batteries (20 hr rate) and about the lightest. You need light weight to not be excessively heavy in FW.
For salt water you can use slightly heavier batteries and the scooter will still be basically neutral. The powersonic PSH-12180FR is the "high rate" 21Ah version of the above. Slightly more capacity in the same case. Slightly heavier which is ok in salt water.
Spec sheets available for both here:
Battery Store/TNR Technical your Extreme Batteries Source
Aftermarket chargers
These folks have good prices on 2 and 4 amp chargers. 2 is very slow, but 4amp a good compromise size.
24 Volt Battery Chargers: BatteryMart.com
Burn tester
If you want to track your battery capacity you can build a burn tester. Don't use it too often you'll wear out the batteries. Just use it to log relative performance. I only burn down to 20.5V under load. I got about 53mins on the 21Ahs and 48mins on the 18Ahs
Gavin/Irvine Scooter Burn Tester
Operating tips
You can make the tow cord a bit long and wrap the excess around the left handle. Most of us drive the Mako/Gavins with the right handle in the 12 o'clock position.
Be sure to soak/rinse the clutch area well after saltwater dives.
Ok gotta work now, hope these prove helpful