[QUOTE=sailor;3326611]Ah well, never hurts to try - spray penetrating grease for general maint. is the ticket - WD-40 as you tried to free up something that's already not working well.
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i felt really frustrated to go and pay a lot for a repair that i wasn't sure at all if it was necessary in the first place! not quite in the mood to open the door's inner cover and try doing something myself either although i am capable of doing it ...
so i thought i'd go online to find help in the virtual world and then i read Sailor's message here, which made me think twice before moving with those other solutions. and it's worked great for me so far!
at first i did try to lock/unlock the doors multiple times while manually tampering a little with the latches too. i also tried the little white colored plastic 'kids safety lock' knob thing that's there close to the latches too but it didn't help really, so i tried lubing it as per Sailor's suggestion. this action didn't show any results at first but i knew i had to leave the lube there for a while to work its way through ... (i think Sailor did mention that too, right?)
now, a couple of days later, today, the door (rear passenger, right) appears to be working fine just as in the past! i hope it won't go wrong again and many more thanks to Sailor for the great suggestion made here!
in case anyone is interested to know how and why that door's lock went out of order, it happened like this: my sister was sitting there once and as i stopped the car and wanted to activate the main unlock button at the driver's side, she also tried to open the door at the very same time: a perfect synchronization of both actions so to say, albeit quite accidentally! i'm not sure if the door did go bad right there and then but i'm sure it was fine before that ...
for the worth of it though, that's the trouble with overly automated mechanisms of this nature: they're not very reliable; also hard or impossible to repair and when repairable, very costly: this could cost me nearly 400 bucks if i wanted to get it done at the dealership!
at times like this, i highly recommend everybody to try the lube solution first before dismantling the door. it may save you a lot of costs and trouble indeed.
btw, the lube i tried is a mini can of spray i bought at a 99C Only store. it's not WD-40 exactly but it says it's a replacement. sounds like it's true.