Quite often there is confusion regarding the Skill Test to be taken. It is not the PPL Issue Skill Test (2+ hrs) but the same as the Profficiency Check you can take in lieu of experience (about 1 hour). Section 3 navigation is at the discretion of the examinier and after 13 years will be a bit longer than if you had more recent experience. So training to pass the test listed
here
There is one other issue after 13 years and thats the RT licence. You will need to retake the exams in accordance with LASORS B1.6 to get the FRTOL re-issued.
The holder of a FRTOL expired for more than 1 year
but less than 10 years, will be required to pass the
theoretical written examination. To renew a FRTOL
that has expired by 10 years or more, applicants will
be required to pass the practical Communications
test and theoretical written examination.
The holder of a UK national flight crew licence with
lifetime validity, who has not exercised the
privileges of the FRTOL for a period exceeding 10
years, will be required to pass the practical
Communications test and theoretical written
examination in order to renew the FRTOL.