Conflicting opinions about repairs to old brick foundation

I have talked to 3 local people and have had 3 different answers, and am trying to find some more input or some clue to help me determine which way to go. I have an old, but not historic, home.

The problem is a circa 1850 (or earlier) foundation wall in need of repair. The three opinions are:
1) it is absolutely necessary to analyze the mortar and use a precise mix to match or the bricks will be destroyed (contractor with experience in historic restoration).
2) it is okay to use a pre-mixed mortar with additional lime added to soften it (mason who has been 'repairing walls like these for 30 years and never had a problem').
3) using pre-mixed from the store is fine. Anything else is a waste of time and money (retired contractor who is a friend--although this seems the least likely choice to me).

So, in trying to figure out what to do, I've done lots of reading. Most on-line and library materials discuss brick homes, not brick foundations. The focus on mortar analysis (opinion #1) seems to be more about what sand was used so that the coloring will match for historic restoration on brick homes as opposed to simply the proportions of lime/sand/cement (if any) in the mortar. The articles focus on appearance issues from not using the right sand mix, although they do stress not using mix with Portland Cement on old brick. Very little, if any, of this repair that needs done is external, so I am not concerned about finding the right sand for a color match. Does anyone know (or can point me to a resource) about mortar analysis in terms of getting the mix exact? How critical is it to get the mix of lime/sand/cement precisely the same as the old mortar?

There is discussion of the bricks being destroyed by using a mortar with portland cement, and I'm unclear if using a pre-mix with additional lime might result in a crumbling foundation in the future. (Is portland cement the only kind of cement used in mortar or are there multiple types?) The mason (opinion 2) thinks that brick destruction is more an issue with an external house wall that faces temperature extremes, not a foundation wall that is largely underground.

I would appreciate any additional information/insight anyone on this site might have.

I'm no expert on this, someone else may chime in. I think you have bits of truth from everyone mixed with bits of lore from everyone.

Bricks, if re-using old brick, can be destroyed by using modern mortar. My understanding as to why has to do with the hardness, and therefore the porosity, of both the brick and the mortar. Using hard, new mortar, with old, soft, bricks will cause mosture issues in teh old brick which will lead to spalling. This is especially true in climates with freeze thaw and when they are outside, exposed to the weather.

So, I think they ALL are right to some degree. The last guy can likely get away with regular stuff because its not exposed to weather extremes. The first guy is trying to be most respectful to the original formulation and his approach will work just fine but be costly. The middle guy will possibly come up with something similar to the first guy and his approach will work too because, again, its not exposed to the weather.

Since this is a foundation, inside, unseen - I think you could even consider just re-building it with cinder block, new brick or even concrete and avoid the whole thing about new wineskins and old wine.

I'm not a mason, nor have I played one on TV. I expect a more informed expert to chime in.