i have never heard this claim about the DSS. have any sources?

As for the Torah, yeah, it's garbage. The existence of the LXX allows us to see places that were clearly changed. The fact that almost all modern bibles are based of Masoretic translations is a complete joke. As a simple example of the lunacy, the correct timeline from Adam is about 7500 years before present, where the Masoretic places it at 6000. This greatly augments things like Noahs flood, and who was alive to see how many generations of offspring. It also directly contradicts known things events like the creation of the pyramids (the flood wasn't global so whatever) so for people who think the flood was global (again, it wasn't) it makes them look foolish.

tl:dr, jews are Satan, they lie, don't ever trust them.