alot of SC also have this problem, u have no choice but try to befriend with the manager and call them lookout ur car for u ... or u just stand guard and watch over them servicing ur car ....
its normal it happened to my sis's myvi at her 5k service last january ... lucky my mom was there, scooted the whole perodua center and the manager quickly change the whole bonnet (bonnet have a large scratch + dented), the manager say it was us who bang it, then my mom said this "if it was us to bang it, wont u be running to us telling us to change when our car just arrive?" ... everyone in the center was looking at the manager "dimalukan kao kao", heck the manager don even know how to speak english properly and my mom doesnt understand much malay so my mom just bomb till they agree to change...
if u r brave enough, take ur car and service outside but u will void ur warranty ... if u have enough patience, stand there and look at them (too bad u r not P2 coz max service 1hr else all free) ...
felt sorry for u Hypro ... maybe u can try search around and try out other SC (i am sure the booklet or watever got all SC imprinted) ..
when u step in, take picture in front of them, and tell them wat happen at the previous SC so they would try to avoid .. else just bomb them ...
@jiayong, i see u had read the link i posted regarding the air intake & exhaust mod guide ... try read the whole thing, everything is explained in it ... further questions u can either ask in that thread or here ...

@masao, got pic ah? ..hehe
@haz, thanks for the info ... will search for it now ... just back form lunch digesting ..