There should be 0 settling going on in a 120 year old house. If it's still moving then there something else going on.
Some of the most common issues will be rotting rim beams. failing piers, not enough piers, to long a span on the floor joist, fungus or insect damage under the house, poor dranage around the foundation. I personaly have never found an old house like that with out at least one of these things going on. Most of the insect damage will be in the area caused by added on decks, additions, mulch pilled up againt the foundation, no gutters or stoops installed tight up againt the foundation.
Any local exterminator can do a free inspection for you. I stongly suggest not using Terminx or Orkan.