Huge thanks to Maureen for this link -
it appears that the MoD has the papers for Stanley Gosling. Or, at least some of them.
Follow her link to
http://wiki.fibis.org/index.php/British_Army#Army_personnel_serving_after_January_1921 and then, following the instructions there, you can go to
https://www.gov.uk/government/publications/foi-responses-released-by-mod-week-commencing-1-december-2014. Scroll down a bit and you'll see sheet "Attachment 3: service personnel indexed data for those with a date of birth date prior to 1901".
You can download it and open it up in Excel or similar and have a look with a find type command for this line:
Item ADT000285562 (I have no idea what that means) with Service Number
3950735, Name
Gosling SJ, and Date of Birth
1899-11-14. This matches your GF by name and date of birth. It means that the MoD has at least some of the papers for Stanley Gosling. If you want copies, you should follow the instructions on the first link that tell you how to apply to the MoD (the FIBIS site only has the instructions, not the papers!) - the MoD instructions that FIBIS points to are on
https://www.gov.uk/guidance/requests-for-personal-data-and-service-records It takes months, by the way.
You'll need to use Service Number 3950735 to apply for his papers. I've no idea where it fits into his history but
http://ww2talk.com/forums/topic/4837-army-number-block-allocations/ indicates that it was a number issued by the Welch Regiment, which also fits your GF - whether it is a Territorial number I've no idea.
What the MoD papers will consist of, I've no idea. It
might be that they include his WW1 papers as well as his later service. People seem unsure whether it's normal for 2 sets of papers, for 2 distinct periods of service, to be bundled together.
If your GF didn't tell them about his prior service, then of course there'd be no reason for them to go and find the previous set.
Best of luck. There is no other way to access these papers by the way, other than by following the MoD process.