Orks (being crude fungus-based lifeforms) reproduce through spores, which are consistently released throughout their entire lives. These spores grow, multiply and eventually produce first varieties of edible mushrooms, then Squigs who feed on these, then Snotlings who cultivate the mushrooms and squigs, then Gretchin who establish the foundations of a settlement and finally the Orks themselves. The end result of this process is that when the Ork emerges he is already in the young adult ('Yoof') stage and a minor fully functional ecosystem consisting of smaller orkoid species has grown up around him.
In any Ork settlement of significant size, hundreds of spores are dropped daily and a certain percentage of these spores will contain the necessary genetic code to produce Orks with innate knowledge of mechanics or medicine (Meks and Doks). These spores are not necessarily dropped by those Orks, any spore can create this genetic material based on the needs of the society around it, ensuring an even distribution of Ork castes. Even if the society leaves, is destroyed or otherwise removed, these spores will still mature and no doubt contain all the necessary elements to create a fledgling society fully able to support itself.
The only way an Ork Clan could conceivably exist without Meks or Doks would be if all of these individuals were killed en-masse. But even so, within a year individuals possessing these genetically engineered skills would emerge in the society once again.
Edit: This is my 1111th post. Awesome.