Taking a look at the Numrich Ruger sr9c schematic, it appears that the whole sight base is not pinned inside the dovetail. From what I see on the schematic, there is a sight base and then the upper sights which are pinned and screwed to the sight base (not sure if that is the case in reality). First, have you contacted Ruger technical support which is generally rated as excellent? If you have the problem with the original sights, they will make it right maybe by sending you a part or having you send the parts to them for installation.
The second, is that generally the way to tighten mechanically a dovetail in a slide or barrel etc. is to carefully peen or swage the dovetail (either the slide or the base) to tighten the wedge relationship. You can probably find a youtube video etc. in relation to a 1911 or other type dovetailed sight for a guide. As a general rule, work on the cheapest part (the sight base) to replace if you screw up unless it is fragile or involves tritium vials-night sights). If you do not know what I am talking about, try a gunsmith as this is regular type work for them and won't be that expensive to fix.
I'm sure that you could also try some type of loctite but some are more susceptible to commonly used solvents than others and you must select the right one for the purpose (not the stuff for screws and bolts). Before buying any of it, try going to the loctite website and reading their technical stuff on what they sell. Remember, different loctites require different temperatures with some approaching soldering temps.
I am currently running an experiment on mauser open barrel sights using this as the primary way to secure the sights to the barrel instead of soldering but unsure about the longterm durability of the product in this fashion.
