#18 is the delay valve. Not the SMC.
2007 Honda ST1300A A LEFT FRONT BRAKE CALIPER ('07) | Ron Ayers
The SMC would be part #2 in the above link to the left front brake caliper fiche.
You would also need part numbers 23 and 24. These are the pivot bolts which accoording to Honda have to be replaced every time they are removed. Some people use loctite and re-use them, but since you ddon't know anything about the bike's history, I would get new.
You also need a handful of copper/aluminium washers for the brake hose banjo unions. 2 per joint. I think that makes 6.
Check the year of your bike from the label under the seat. The design of the SMC changed after 2007.
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Edited version of the image on the fiche showing parts #2, 23 and 24.
Part #2 comes pre-assembled - like this 2009 version. Beware the different part numbers. Before 2008 has the number 06454-MCS-G03. 2008 and later, the SMC ends R02.
They are very different, but it is difficult to spot in a photo. The pre 2008 versions have a small hole in the casting on the side, just below the rubber boot.
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Part #18 on your link is the delay valve - is located behind the right fork leg just above mudguard height. It is a device that stoped the rear pedal applying the centre piston on the front right brake caliper at 'normal' pedal pressure. It opens up to add extra braking force when the pedal is pressed harder.
This has nothing to do with the SMC.