zhivuyatut

I would not top off usually. But when on a road trip across Utah or Montana - that couple gallons may decide whether you would make it to the next pit stop or not.
Charcoal canister is just a tin box packed with absorbent, you cannot do it much harm by overfilling your tank occasionally. But there is a lot of valves and hoses going in and out. Constantly drenching them in gasoline would eventually cause them to fail.
The dealer of course would not try to find the cause - just replace the whole assembly.
Here is an interesting read on the topic:
http://steampunkworkshop.com/toyota-...s-valve-repair