CRT Monitor No Picture ! Contact Enhancer ?

I have several smart 19inch CRT Monotors. Branded Xerox and Philips but apparently identical. Model No XA7191.
All exhibit the same fault screen illuminates but no Picture. Problem bas been identified as the ribbon cable connection,
internal monitor VGA Board to screen. At the screen end the cable is secured by two blobs of "heat glue". When glue removed and connector cleaned, monitor worked properly on bench for several hours. Cable than re-secured using heat glue and monitor re-assembled (reassemble completed with power on) Montor still performing perfectly. Power then switched off and then on. Back to original fault (Screen illumuminates, No Picture)

The above operation repeated on two additional monitors with identical results !!!SCREAM!!!

Any Ideas ? Before I throw them in the skip
Does anybody know of a low cost "contact enhancer" that I can use on the ribbon cable ?