X2Go is fixed on Mint.  The apt-add-repository ppa:x2go/stable repository creates a .list file containing the xenial repository which makes sense as Mint 18.3 is still based upon Ubuntu xenial, but the xenial repository does not work, neither does yakkety or zesty although x2go will install from these.  Finally I tried artful, x2go both installs and functions under Mint 18.3 if you use this repository so it is again operational.