Your flaw is going to the shop/ BM .
I’ve done this . They don’t have exactly what I need so I buy ‘nearest’ thinking I can improvise .Get back to base and realise it won’t work so order online . Online stuff arrives 2/3 days later . Realise I’ve ordered the wrong stuff . So package it up to take back to PO and then drive to BM knowing they have what I need ! . Get to BM ; item is out of stock . So get home and order item online .
So it can take weeks just to get some basic materials/ parts on site 😁