The reason I chose 5.0.18 was that it was the only other option in the repository and I am more happy to stay within the bounds of what they have authorized.Due to the latest changes in VirtualBox
kernel 4.13.0 is not compatible with VirtualBox 5.1.34 and
kernel 4.4.0 is not compatible with VirtualBox 5.1.34 due to the latest changes in the kernel
kernel 4.13.0 not backwards compatible with VirtualBox 5.0.18 but
kernel 4.4.0 is compatible with VirtualBox 5.0.18
The incompatibility of VirtualBox 5.1.34 is caused by Oracle phasing out support for running in 'raw mode' so that system without VT-x can no longer run VMs. The lack of backwards compatibility of kernel 4.13.0 is not known to me (being a non-expert).
I have requested Oracle to provide (and support) a 'heritage' version (see: viewtopic.php?f=7&t=87387).
However, the fact that VirtualBox 5.0.18 is in the repositories (i.e. listed in Synaptic) means that kernel 4.13.0 is deemed to be compatible with VirtualBox 5.0.18.
Will you pass on to Oracle my request to provide a heritage version?