Yes, the advancement of the perihelion of Mercury is greater than predicted by classical physics but in accord with the prediction of General Relativity. Perihelion is the point in its orbit that’s closest to the Sun. This point very gradually moves forward along the orbit. The difference between its actual change and that predicted by classical physics is only 43 arcsec/century, which is not very much.
You can probably see a transit of Mercury with just a Sun filter (no telescope), but I think you’d need one to time the transit to sufficient accuracy for calculating this effect. But it wouldn’t have to be a very large telescope. Le Verrier calculated it using measurements from the 18th and 19th centuries, a time when all they had were small telescopes, at least by modern standards.
Observing Mercury with just the naked eye would be enough to measure it, but it would take a couple centuries of observation just to see a change in its perihelion. To be able to detect the difference between GR and Newtonian change would probably take about 10 times as long.
A more direct way of seeing relativistic effects with only a small scope is to observe gravitational lensing. The Einstein Cross can be observed with an 18-inch scope at a dark site. That size scope is very small by professional standards, but large (although not excessively so) for amateurs.
