Very interesting. Assume one of these. The 3mm base thickness and size look ok but it is not clear how the short tube which is part of the base into which your 25mm od diameter stanchion tube fits is suitably secured to the base. The L shaped rod which is secured to the short tube side at its upper end is welded to it so great, but the securing of this rod to the 3mm base is not clear either.
www.ebay.com.au/itm/324658872721Suggest the words "reinforced, pressed 304 grade stainless steel" need to be clarified.
So on a Swanson 31 - are they of original age? 304 is not as good as 316 corrosion wise but many stanchions and bases of 304 are still around 40+yrs later.
The photos seem to show no welds between the base plate and the short tube or lower end of the L shape rod. The short tube seems to have been turned neatly into a shape to fit down inside the 3mm base chamfered hole. Maybe "pressed" means that the short tube and the rod are pressed into the base and somehow radially expanded outwards from their underside ends to make an interference fit with the base. This could work with only mainly compressive vertical loads down on the stanchion but of course the stanchion posts will suffer lateral bending (outboard and inboard) and maybe some vertical upwards loads through their life. So it is very unexpected to see no welds around the short tube to base connection, or the lower L rod to base connection.
Are all your stanchion bases like this? Do any have welds apparent at these junctions? If not some others must obviously be loose? You could take them all off and weld them up yourself with 2mm ss rod and $140 welder.........like I am doing now wth 316 tube and plate but need a lot more practice to get the welding right.............if you had to renew all the stanchion bases it would cost an arm and a leg - you might have a welder mate or a local mens shed who could easily do the welding of these for a lot less than that. Clean all the 40yrs surface residue off properly first. Seal up the top of the stanchion tubes - plugs can be bought - and use sealant in the lifeline holes to prevent crap getting down into the stanchion tubes.
Sorry if I am missing anything in the photos. Look forward to your response.