Are the rules proposed by Slater for the calculation of effective Z right?
Slater's rules are pretty good, but they're not perfect. Consider that he published his work in 1930: Phys Rev 1930 v. 36, 57
There are a number of people who have modified Slater's scheme to better reflect shielding effects and correct for experimental ionization energies and electron affinities (and similar properties) in later rows of the periodic table.
If I remember correctly, one such modification is that d and f orbitals shouldn't have as much shielding as suggested by Slater, but the correction is small. There's another scheme that uses an exponential correction instead.
For example, Wikipedia gives effective nuclear charges from Clementi and Raimondi, who did full self-consistent quantum calculations and you can compare these to Slater's.
The main take-home from Slater's rules is that they work pretty well for a wide range of elements, including 1st, 2nd, and 3rd row. I think the corrections generally tweak things when we get into the 4d and 5d transition metals and some of the lanthanides and actinides. Not bad for an 84-year old paper!