Not sure if the ST1100 and ST1300 gear lever mechanisms are similar ot not, not sure if this helps.
The ST13 has a series of rods that connect the gear change foot lever on the LH side of the bike, under the engine and gearbox to the the RH side of the bike. Three rods from memory, with little knuckles which slip over a ball joint, and the rods have a female LH thread one end, a female RH thread the other. Rotate the rod and it tensions the mechanism, or loosens - whatever is needed. There's a 10mm (could be smaller) lock nut both ends.
Hmmm ........ hoping you can follow.
On the ST13, one of the rods came loose and the foot lever flopped around. Lucky I was in third gear and I could get home okay. Took about two hours of cussing and cursing, skinned knuckles, but I got it re-attached, tensioned and lock nut secured.
The rods looked some thing like this.
Checked Partzilla, could not find them.