3rd jen Suzuki Jimny central locking system

hi,
I have a 2013 Suzuki Jimny. The central locking system is not working 
It is driving me crazy crawling to the back of the car inside to unlock the rear door because it does not have a exterior key insert to lock/unlock. 

I'm the second owner. The first owner lost the remote for locking system. He installed a aftermarket remote lock for the car. he did it himself. when i got the remote the locking/unlocking sometimes worked on and off. it had a mind if its own. if i insert the key this never unlocked all 3 doors. the remote unlocked all 3 when it worked. 

Now the remote does not work at all. i don't think its the battery on remote. i took it to an auto electrician. after looking at it he says the door locking module for Suzuki Jimny has leaking capacitors and is stuffed and should be replaced. he shows me the circut board and it has yellow parts around it apparently from the capacitors. this is the P/N 37190-81A70
on the part it is called "Keyless Entry System"

he says that once this is replaced the central locking will work and maybe the remote. a new one is like $1300!. i can't afford this that's almost what the car is worth lol. 

I have looked at wreckers for the part and i found 1. plugged it in and nothing happened. maybe it was faulty two. where i am located it is very difficult to find wrecked Suzuki jimnys. the ones i do find they dont know what im talking about or they try sell me the whole locking system immobiliser, door locking rods, etc.. for $600. if the do understand the part i want they say it wont work because its wired to the immobiliser. I have the system unplugged and i can still start the car and drive. 

seeing as i cant get the part i went to a computer store and they said they will look at the board and fix it if anything is wrong with it. they said that the yellow stuff which is supposably capacitor juice is not and is normal and should still let the board work. i am waiting to hear back from PC store. he said it looks like it works though so it could be something else. I don't understand how and why its so complicated for this whole system for this type of car. maybe im going about this the wrong way or have overlooked something. i dont realy car about remote locking all i want is to be able to unlock the rear door without having to crawl inside and manualy unlock. i just want the key inserted to unlock all the doors. 

i attached a photo of the "Keyless Entry System" part that might not be working

if anyone can help me it would be greatly appreciated. just and idea or similar experience might be helpful. 

many thanks

The first thing is to verify the function of the door switches, the same ones that operate the interior light. A faulty switch or a door that doesn't engage with it properly makes the system believe a door is still open.

I think that mechanic is having you on about the remote central locking module, I've never heard of one "leaking from the capacitors" and mine (2008) was working up until I sold it a few months ago (I swapped in a JDM module so I could unlock/lock on one button).

Have you tried re-registering the fob with the vehicle? The instructions on how to do so are here.

And just to be clear, when unlocking the driver's side door, all three of the doors on the vehicle unlock?