R129 - 300SL 1990 Intermittent remote door locking problems

[coma]

Still trying to get my intermittent remote door locking problems resolved.
This is driving me nuts !!!
Just spend north of $1000 bucks with an independent repair shop here but problem still persists.

Have already searched multiple online forums for a solution to this problem. Found that a number of people had similar or identical problems in the past, but no final root cause analysis or remedy was ever published.

HOPE THAT SOMEONE CAN POINT ME IN THE RIGHT DIRECTION.

Here are the symptoms of the problem:

* remote locking function works completely intermittent
* works more reliably at night / when dark outside
* works sometimes just from driver's door, but not on passenger side or trunk
* works sometimes from driver's door AND trunk, but not on passenger side
* occasionally when using the key in driver's door lock the red or green LED indicator
lights stay on for a long period of time (overnight).
* when re-seating the connector on the IRCL controller sometimes everything works for
5 minutes
* key stopped to operate trunk lock, but red or green LEDs are flashing
* when using remote the red LEDs sometimes flash longer than the green ones

Here's what has been done already (failing to resolve the problem):

* replaced key batteries in original key and synchronized the remote
* bought and synchronized new key (on recommendation of repair shop)
* replaced all fuses in the car and cleaned contacts
* cleaned connector contacts of all accessible control modules (including IRCL
controller).
* polished all external remote sensors
* repair shop checked car diagnostics, but no clear result

Questions I have:

* do the symptoms point to a defective IRCL module?
* do the symptoms point to other potential connectivity issues - which ones?
* is there a way to check if the IRCL module is bad?
* if IRCL module is bad, can it be replaced with a used one from another car or is the
module coded to the specific car?
* any other thing I should have checked?

THANKS MUCH IN ADVANCE.