Moderns can be soakered , stonewolds can too. Just not a big standard soaker. Fitted under the tile but formed with an upturn on the under edge. its been covered here more than once .
As I said (before the troll staggered in and got it all wrong as usual - come'on troll, buck up with your googling - amateur boy) individual soakers go under individual abutment tiles and cover flashing comes down to protect the soaker upstand.
Not all tiles take soakers eg profiled tiles - so post a pic of what you've got.
Do you have any signs of water damage?
There's no reason to believe that there are soakers under the lead in the OP's pic. That would be very odd and a bit expensive belt & braces approach.
My tiles are almost a copy of modern/stonewold, actually they are a bit sleeker, exactly like the richmond 10 / edgemere. By following links I have found Marley do a plastic soaker for Moderns/Edgemere and there is a very short video on the Marley website, but I do not understand how it works. https://www.marley.co.uk/accessories/soakers
As I said (before the troll staggered in and got it all wrong as usual - come'on troll, buck up with your googling - amateur boy) individual soakers go under
Yet Marley's own soakers go over their tiles - do tell tell
Marley say that their Dry Soakers can leak water if driven from the sides, and the soaker depends on its sheer size (width) to prevent this (but there are none in stock anyway).
Soakers however generally sit beneath a tile and are not used on profiled interlocking tiles - rather, they are only used on flat interlocking tiles (and all other flat tiles, slates, plains etc) because of the risk of driven rain etc.
Marley (Moderns) produce their own proprietary soaker that sits on top of the tile.
Profiled IL tiles just need a cover flashing that extends beyond the first profile.
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