To answer the question you posed - you are the skipper, so yes, it's all down to you.
(At a guess, the sikaflexed windows will probably be the most trouble-free part of the boat)
A moment's thought will make it clear that a niche engine builder such as VP does not have the scale to manufacture their own anti-freeze, in the same way that they do not produce their own oil! Your local car parts shop - or even Halfrauds - has what you need.
Stating the obvious - if it was running perfectly up until you changed the filters and now it is not, there you have the most likely culprit. Something has not sealed correctly. Re-check all the seals.
The danger, of course, is that the insurers will have a reason to wriggle out of any claim by saying that you have failed to comply with their recommended maintenance schedule, however ridiculous.
I have been using Patio Magic for years. It is very good at getting rid of algae/moss/greencrap. At its recommended 4:1 dilution it has never had any adverse effect on a wide variety of fabrics I have deliberately or accidentally sprayed. I have never knowingly used it on hide, but I doubt...