No sponsor is correct in that you can do a test with an examiner. However, he is incorrect in saying that "6 [hours] must be as PIC in the preceeding 12 months". All 12 hours must be within the preceding 12 months, and 6 of those must be as PIC.
Note that you do not actually need to do anything to keep a PPL current. What you are actually doing is keeping the SEP(Land) rating on your PPL current. Once you realise that, it's easy to find the rules: they are in
LASORS, Section F (which is the section about Type and Class Ratings). Lots of details in there, including the full rules about revaliding both by experience and by test, and also how to renew the rating if you go past the expiry date.
FFF
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