can consider buy online/postage, then bring workshop ask them help pour (after ATF drain, and after pour lubegard fill ATF to appropriate level)

best if you pour it during a fresh gear oil change interval not after gear oil change then drive maybe 500/1000 km or more.
if in doubt, consider performing ATF flushing prior to lubegard + fresh ATF especially when you mentioned that your car is flooded before, since water may easily enter the gear box housing via the dip stick (not sure bout persona, iswara dip stick is just at the gearbox housing which is damn low lol.)
more so when you described that changing ATF improved on your problem

and yeah, give a try to these solutions, at worst you waste rm90+, however more often than not if it's confirmed to be stuck valves, lubegard can help solve that and you'll save over rm400 (not including replacing worn parts if reqiured) in repair bills and car down time.

again, don't straight away put in. do ATF flushing (if you can afford), else just drain your ATF, pour in lubegard, then fill with ATF till appropriate levels.
DO NOT OVERFILL, please fill till cold level, then to make sure, start engine and drive a bit or if car is jacked, have the gears cycle a bit between reverse/D/P and check again on the ATF hot level.
if on really tight budget, go with proton's ATF SP3 or XP3, else spend a little bit more for Caltex ATF-J (need to find at caltex stations)

AFAIK false, the mechanic probably con you... however if you're uncertain of the gear box ATF filter quality (since you mentioned black oil poured out before having repaired/replaced by black shop), can consider replacing the ATF filter which means you need to remove the ATF oil sump.
Buy original gasket/ATF filter from proton parts stockists/glenmarie parts center

no need to use lubegard flush, just regular atf filling, let it run/cycle in the car, and drain it out. there are workshops that have dedicated flushing machines which will work better, however expensive charges.

Eneos Kepong: http://twitpic.com/drphpi