No tools are required. Just use your finger-nails to pry off the case along the line (red arrow). It's amazing that Garmin only used glue to assemble the unit.
The display and the bottom are separated. There are no wires in-between. They are connected thru some pins.
I also found no O-ring between two cases. Well, as I can pry it off easily, you can imagine its capability in water-resistance...
Indeed, I found water inside the case. The up/down-arrow keys (the soft-plastic keys) stored some water (not moisture only). It's not on the circuit board or battery anyway.
The GPS antenna is at the left-hand side, wrapped in silver plate.
The battery is sticked by 2-sided tape. It's a 3.7V, 750mAh Li-ion battery.
Does it look like the 4th-generation iPod battery?
Believe it's the SiRFIII chipset under. Note the golden contacts for connecting to the battery.
The micro-switches (up/down arrow, and enter).
I wiped the water and let it dry for a week. Then I temporary fixed the case with scotch tape. When I turned it on again, amazingly it worked again (although the up-arrow key didn't work at all).
I used it to have a 20km test run...
Unfortunately, because of the hot/humid weather, my sweat 'melted' the tape and suddenly the cover fell on the ground. I had 3 pieces... the cover with the display, the attenna, and the remaining battery with the wrist strap.
I thought it was a 'total loss' and packed everything back home.
Then I found all parts weren't broken and it's just the connector loosen between the attenna and the display.
Again, there were plenty of moisture (sweat) inside. I removed the battery this time and found the speaker (buzzer) was totally eroded. Ah... that's why I found the level of 'beeping' sound went lower and lower.
The salty water (my sweat) actually went it from the 4 tiny holes at the back, eroded the buzzer and then the micro-switch.
I cut the wires of the buzzer and blocked the holes with strong glue.
To disable the up-arrow key, I used a knife to cut out the switch.
Again, I put everything back and tried, haha, it's still working. This time I carefully cleaned the case and then glued them together with silicone sealant (the one for decoration, usually used in the bathtub, kitchen, etc).
Now the unit is survived. Without the up-arrow key, most of functions could still be used (navigated with down-arrow instead). The only problem is that I cannot increase the screen contrast as it requires the use of up-arrow.
Without the beeping sound is not a big deal at all. At least I can keep using it until the new model is out...