Just to put this to bed, after an awful lot of faffing about the LGV is now shooting beautifully with a TX spring, exactly as predicted in the article and at 10.6 ft lbs with 36 mmpreload. As might be expected, BTDT correctly diagnosed the problem at the outset, but I was distracted by fitting a 25 mm Weihrauch seal, which was a much better fit but only gave 8.6 ft lbs. With the carefully resized original Walther seal, now an easy finger push, and with a guide made by Mr Bum for my LGU when it was running a TX spring and a new delrin top hat, made on my woodworking lathe using wood turning tools, there is no trace of twang and it feels beautiful.

Grateful thanks to all who offered advice.