I ride a 2008 st1300. Last year the alternator failed and this year the coolant hoses were brittle so i changed them all. Now i have a oil leak from the water pump and its burning oil when i accelerate. So its time for a new bike as its my daily vehicle and i cant be without one due to work.
Im tempted by another ST1300 as i have worked on them plenty and can swap the mods to the new bike with ease one cheaper than the FJR
Im tempted by the 2013 gen 3 FJR1300 for the cruise control and less heat no idea how hard they are to work on though
Day to day use is in town 20 minutes each way monthly use is rallies around 200-300 miles away
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So if the panniers will hold my Nolan i will go with the FJR1300 run it faster daily with topbox only and then monthly with full luggage using cruise control. My Broken St1300 will get time to be fixed and will become my backup bike
The reason I have owned five ST1300s, was because I was commuting 125 a day.
After putting on 140K miles on my first ST1300 (2005), around 2012, I decide that I needed a ST1300 with less miles for long trips and just continue using the 05 for commuting and have the 04, also as a back up.
But then a year later (2013) I stumbled on a 2010 with 1,500 miles that was wrecked, but not totaled. And a year later (2014) yet another wrecked ST1300 came into my grasps.
Like you, I became very familiar with working on the ST1300s and I started accumulating extra parts and then some more extra bikes (three of which I had to get rid of).
My suggestion, IF the ST1300 satisfies your needs, and you already have one that you wouldn't get money for anyway, why not look for a low mileage ST1300 (you might have to replace a few things on), and stick with them.
Good luck on what you decide.
BTW, I don't remember seeing how many miles you have on your 2008 ST1300?