When it rains, it pours

[max]

Scary stuff Ferret, reading up about this ( thanks for the links guys ) You are right, it does look like the smc plays a big part in this, to move the caliper assembly back far enough to release the break fluid pressure it only relies on one spring behind the smc piston.
If that does not go back far enough the front caliper engages which causes more pressure on the smc piston which engages the front calipers ....... so you end up in a vicious circle.

one guy ( 4jranch ) found something interesting;

ST1300 - Secondary Master Cylinder Rebuild- SMC

Secondary Master Cylinder Rebuild- SMC

This is a job that probably all ST1300's over 5 years old need to consider. A regular addition of silicon grease into the outer boot might be excellent preventive maintenance. Forest had warned me of this problem but I really didn't understand the problem until Lynne's rear brake began locking up, enough to damage the rear disc and toast the rear piston seals. With a more thorough research of this site I was able to understand the problem. This really helped as I was able to direct the service manager as to the real problem when we took her bike in for repair under the extended warranty. The repair took three weeks but was finally completed. I felt that I needed to get mine done before my ST had similar results. I would recommend doing this job when you are replacing all the brake fluid.

Good points and this area under the smc boot which may be overlooked, is the place where some leaked brake fluid builds up, attracts moisture and goes to work on the parts around it, and over time......

And i am with popgun on this; replace, this small release hole can be blocked over time and it is vital, just my unqualified 5 cents, sorry guys, i get carried away sometimes.
Cheers ferret; max