Remove space in reference in “et al. ,”

Question

I'm using Sharelatex to work on my thesis, and I want to use the natbib package and authordate3 style for my bibliography. For some reason, when referencing a bibliography entry with multiple authors, I get a space between "et al." and the year.

Here's a minimal example:

\documentclass{article}
\usepackage[utf8]{inputenc}
\usepackage{natbib}
\bibliographystyle{authordate3} 

\begin{filecontents}{biblio.bib}
@book{jon99,
    author          = "Tom Jones and
                        Jack Smith and
                        John Doe",
    title           = "Wonderful Book",
    year            = "1999"
}
\end{filecontents}

\begin{document}
\citep{jon99}

\bibliography{biblio.bib}

\end{document}

In Sharelatex, this gives:

Now, I've looked around, but the only solution that seems to work is by manipulating the authordate3.bst file (as suggested here), which I obviously don't have access to, since I don't have LaTeX installed on my machine.

I've also tried changing the punctuation separation between the author and the year to include \unskip using \setcitestyle{aysep={\unskip,}}, but that unfortunately didn't work. Simply adding a negative space (such as using \setcitestyle{aysep={\kern-ex1,}}) fixes the space for multiple references but places the comma on top of the author's name for single references.

Answer 1

This is somewhat of a home cooked solution, but I opened the authordate3.bst file in my text editor and replaced the three occurrence of {\em et~al.\ } with {\em et~al.}. My authordate3.bst was located here /usr/local/texlive/2014/texmf-dist/bibtex/bst/beebe/authordate3.bst.

After I did that I ran your code again and all was good (I might have created some horrible problem I am not aware of?).

Below example was produced with the code Martim provided above.