Page 103, Helpers in the Laboratory, middle column.
"...each helper adding his MT and Intelligence scores to the primary researcher's scores."
It seems very straightforward for me.
As others have said. You are correct. Helpers only add their Int + Magic Theory to the Lab Total.
The normal ones that allow you to dispell magic effects --- see the General PeVi guidelines (ArM5, p160). Although as Birbin points out the PeVi spell will need to be of high level to have an effect if the Longevity Ritual is a big one (assuming that the level of the Longevity Ritual is the level of the creating CrCo Lab Total). Penetration itself is not such a problem; that's what Arcane Connections are for.
The other option could be to use a PeCo effect to trigger an Aging Crisis, which will then cause the Longevity Ritual to expire. There is no explicit guideline for this in the core rules however. On the other hand, causing an Aging Crisis seems like a clever effect for a major disease to have; it is a base PeCo 20 effect to cause a major disease.
Dispelling a Longevity Potion should probably be a General PeVi ritual, similar to Cutting the Cords (True Lineages, p. 75)
If you read the whole section it seems very obvious that this is not what that means. The first column on the same page says "...you add the helper's Intelligence + Magic Theory to your Lab Total..."
In this context "scores" must mean Lab Total.
I asked our Guru. He said you have right, Richard. MT is added simply to the Lab Total.
I have to agree with RL & co.
There are two tip offs: one is "scores", plural. The various "researcher's scores" are added together, and the sum is their starting Lab Total - what the author is saying is "add each helper's scores to these scores and the sum you get is the new, improved lab total."
The other (and main one) is in the 2nd paragraph, 1st column, well before Birbin's citation, when the rule is first explained:"...If you are being helped to perform some activity that uses your Magic Theory, you add the helper's Intelligence + Magic Theory to your Lab Total for the season..." (emphasis added)That seems very straightforward to me.
If Birbin's literal interpretation were correct, you would first have to ignore the above rule, and then add all the Helpers' Intelligence Scores to the researcher's Intelligence score - for any and all purposes in that lab project, apparently - and that makes no sense. (Or both scores to both MT and Intelligence - and that makes less sense.) A researcher with a low MT and many helpers does not suddenly have a better grasp of MT than someone with a high MT, they simply have a brute force advantage in getting the job done.
I think this is a case where the writer got casual with their terms as the topic changed (they are leading in to multiple helpers and Leadership), but did not intend for the second explanation to directly contradict the first.