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Segmental retaining walls, like unilock or any of the many, weep between the blocks since there is no mortar. You should have perforated pipe running at the bottom of the cut or fill to carry away water so that it never builds up in the first place. The wall should have well draining gravel behind it from top to bottom. Then there is no water build up, it just goes down to the perf pipe. The perf pipe needs to be able to carry the water to daylight, a drywell, or a leaching trench away from the wall. There is no reason to have a 4" opening above grade on a unilock wall that I know of. This is something that would be done with a poured wall or timber wall. My guess is that the guy who said you needed the weep holes is older or at least old school and not up to speed on segmental wall construction techniques that have been well developed over the last 15 years or more.

At first reading I thought I would be in total agreement with laag. But after some reflection, maybe I'll wait before saying last rites. There are some things I'd like to know, like a better description of the material in his "urbanite" wall section and how thick it is; the width from wall to dirt backfill. And how high up the wall is it to where the deadman attaches and how is the attachment made? Are the upright timbers at the end of an 8ft wall or set back from the end? Are the horizontal planks on the dirt side of the uprights or out on the face of the wall? What is the distance across the terraces between the walls and is the grade mostly flat from the wall tops? What is the climate like? Does the ground freeze? Lots of rain or dry? What will be the land use for this area? What I'm getting at is if the "urbanite" wall is made up of 4 to 8 inch angular rubble and is a little over 2 ft in width, then the wall system may well act as a gabion wall; a mass gravity wall. A basic standard for gabion thickness is 0.7 to wall height. If the uprights were set in from the wall end 1.5 ft, then the middle span would only be 5ft. If the planks are put on the fill side and the deadman braces are well attached to the uprights, this wall might stand for a long time. My guess would be that it didn't get built that way and it's going to fail. It's sad that homeowners don't complete a full plan and bring it here for review before construction.

You could try backflushing them with water from the hose. Not permanent, but it could work for awhile depending on what was used for backfill and the amount of groundwater you have. Are tree roots the culprit? That's a whole nother problem.