A legionary of Legio XI in Britain?

Details of the following inscription apparently found at Marton in Lincolnshire have recently been added to the county Historic Environment Record:

The text is straightforward:
Marti sanc|to sacrum | C(aius) Iul(ius) Anto|ninus mil(es) | [le]g(ionis) XI Cl(audiae) | [e]x voto posu|uit

the context less so. The legio XI Claudia is otherwise unattested in Britain and for most of its existence served in the Danubian provinces. How a serving soldier of that legion comes to be making a dedication to Mars at a rural settlement on the western fringe of Lincolnshire is the immediate, and potentially very interesting, question. Except... the provenance is a little suspect. Apparently found at the edge of a field by someone walking along the lane, reported to Retford museum (at least), but since sold at auction for several thousand pounds.

Could this be a case of a manufactured provenance for an eastern European artefact allowing it to be sold on legitimately in the UK? Seems a large object to transport, but then if it can be worth £3500 you might go to the effort. Mind you if the story I hear is true, then the 'finder' sold it on to someone else who then got the £3500 at auction so either the plot becomes more convoluted, or the initial sale wasn't as lucrative as all that.

Is there any reason to think it real (or really from Marton)? The lane is on the line of a Roman road (leading to the Trent crossing at Littleborough); there is a Roman fort just to the south and a Romano-British settlement just to the north. The fort is assumed to be early and temporary (all that is known is the cropmark of an enclosing ditch); the settlement is more long-lived (quite possibly there first). Legio XI was on the Rhine from about AD70 to the end of the first century and reinforcements from that source not out of the question but we still don't have a good context for an ex voto dedication to Mars just here...