Get some new crush washers for the Banjo Unions. The SMC requires 4, but you will probably need to remove the ones to the caliper too.
I just bought 100 copper washers from demontweeks
Buy Goodridge Copper Crush Washers | Demon Tweeks (demon-tweeks.com)
Since you have to replace them every time you dismantle, its handy to have some in stock if you ever have to separate a joint.
Some will (rightly) argue that you should have alloy washers otherweise you are likely to get galvanic corrosion - caused by electrical reaction by different metals.
But I have had less problems with copper washers than I have with alloy washers which seem to corrode due to salt from the exposed outside edge. I have never seen that with copper washers.
Check - but I think the washers are 10mm Inside diameter.
You might also find this useful - When I last went through the process, I took photos and tried to identify the potential snags. Download the pdf - post #1.
Please heed the warning about disturbing the rubber boot, and how to put it back properly if you do want to add additional silicone grease behind it.
Article [13] - ST1300 Maintenance - Replacing the Secondary Master Cylinder (SMC) | ST1300 Articles | ST-Owners.com
A neat trick I think is to bleed with the crush washers just tight enough to stop fluid coming out when you are bleeding. It gives you the opportunity to burp the joints and still have plenty of 'crush' left for when you tighten them to their full torque setting - 34Nm I think, but as always - check before proceeding with info from some stranger on the internet. Did I check ? Yes, of course I did. But you don't know that. Check yourself !
Don't forget the most important bit - to take apart your old SMC including the nylon cartridge in the inlet port, and report what you find.
Where abouts in the UK are you ? Are you close by - see under my avatar.