Originally Posted by Seb58

Well, things got sorted out... I found a company that sold bobbins with the same reference number than the one mentioned on the user manual (#172336) online for a pittance.
I received them and they work wonders. When compared with the "no-brand" bobbins I bought before, the 172336 ones are slightly less curved and slightly lower and wider. They sit snugly inside the Apollo bobbin case and therefore the bobbin thread tension is adequate.