Old Scubapro. Similar to MK V and MK10 but not quite

[Couv]

With the exception of the damaged DIN fitting it looks like a standard MK5. The socket to remove the swivel retainer should be size 11/16" but note not every 11/16" will fit in into that small space. ScubaPro Lever Height Adjustment Tool review

Colored o-rings, seat etc: It was not uncommon for SP to color code their seals and seats.

Edit with picture of 11/16" sockets. Note the squared off deep socket available from @herman (if you beg, because I don't see it in his current catalog.)

 

[halocline]

Looks like a MK5 to me. Some of the old SP DIN fittings had circlips; they're not really necessary. The TUSA and oceanic balanced piston 'clones' are visibly different, just the design is the same. Parts are not interchangeable to my knowledge.