Sometimes a newly-replaced mechanical seal will leak a small amount out of the weep hole; this isn’t always bad news, however. Sometimes it takes 100-200km of riding to fully seat the mechanical seal. If the leak is significant (more than a few drops/min), however, or continues past this point it may indicate a need to take a look at what’s going on and whether there is a problem.
It certainly pays to be vigilant about leaks and the coolant level for a while after changing out the seal, just in case – but as above, no need to panic straight away if you do find some coolant.