Most of the time?

Or only during cold times?

1. It's the bearing that keeps tension on the belt, last time I kena also... RM 20 only for cheap brand and RM 40 for good one. (without upah pasang)

2. it could also be that your belt already makan...

all in all, parts only around RM 50. direct from spareparts shop. if you go workshop, sure the belt already RM 68... they want to untung also ma..

good question, I don't remember... but it's a bearing on it's own (you can see it clearly) hanging out on a piece of metal stick which is adjustable for the belt tensioning.

looks like this (the shiny metal piece), but note this is for the new saga blm, not the old one... but the sit at the same place.

RM 20 china, RM 40 japan. Installation RM 10. last I fix that for my Old Saga Megavalve was about 1 year ++ ago.

btw, which saga you using?
for BLM correct naming, for Old Saga they just call belt tensioner bearing

is the belt tensioner giving the belt proper tension so it doesn't slack/slip?
how old is the belt and/or if it is having cracking conditions?

consider trying some candle wax on the air cond belt to recondition it which helps a little

ok, then same price. any other price than that... means you kena kencing. 

True, but sadly a lot of original packing nowadays which are cloned parts...

I would normally ask for Mitsubishi or High Quality Made in Japan parts rather than China/Taiwan/OEM (not because they are not good, but afraid to kena clone).

Unless you go get directly at Proton Parts Glenmarie. then sure 100% original.

proton oil filters are around rm10 for single piece/SC/part center glenmarie pricing

if you buy in bulk like a row of 12 (iinm) and from outside official stockists, they can go as low as rm7-9 per piece.

6 seems a bit on the low side especially if it is single piece, maybe you can check it again by lifting the car and inspecting the oil filter.
Iswara oil filters are still using the bigger sized type will all the proton logo/part number (starts with PW then numbers) printed on it clearly.

but oil filter is rm12

how much was yoursS ??

yeah ...same here ...lol ...

Posible sources of rain-water entry:
1) bodywork have holes due to corrosion / windscreen seal leaking.

2) tail-light seals have deteriorated - you can clean
the dirt from the original seal and apply new sealant. Check a few
days later whether the new sealant is holding.

3) capillary action of the contact surface between the rubber lining
and the metal lip of the boot/trunk door. Try this to stop the capillary action:
a) remove the rubber lining/weather-seal,
b) clean the layer of dirt that is now exposed on the bodywork
and apply some polish/wax,   
c) wash/scrub the rubber lining/weather-seal of the same, let it
dry and spray some WD40 or apply grease in the groove throughout
the whole length,
d) instal back.

Taillight seals most likely, you can re-seal them easily with silicone or caulk. 

signal does not work sometime. After some discharge, it works again.

could be wiring loose or something which is suspected.
I was actually hoping for entire blue print layout of our Saga/Isawara model published. 

You mean the bulb as circled? I think the whole unit
is attached by one screw, accessible thru the hole in
the headlamp (arrowed).