Door Locks Electrical Problem

I have 525I 1991, and the doors will not unlock. Have to try many many times before they will work. I have tried to hold the exterior door handle up and tried to manually open with the key but it takes many many attempts before I finally get it to work. ( They will finally work after many many attempts like over an 8-12 hour period). I checked the fusable link under the back seat in the small black box where the battery cable connects but it is in good condition. Any ideas? I will be extremely grateful.
Thanks alot in advance,
at my wits end, Burtv