Most likely you have a barrel alignment problem.

The first step here is absolutely to remove the barrel/shroud. Assuming no obvious damage, clean, degrease, re-assemble and test.

If obvious damage, look for replacement parts. Easy if it is matt finished, harder to find for the older shiny "blue" versions. Try sales here or on other similar fora. Or "ze Germans" for new stuff.

If all that fails, an easy option is to buy the (unimpressive but functional) 11mm scope rail, fit a red dot, and adjust to your preferred range. Unless, like me, you just really don't like optics on pistols.

I doubt:

a) that the genuine Smith sight fits;
b) that it is worth the expense (I'm guessing £50+);
c) that it actually helps at all with this issue.

Good luck!