This is an update to my 6 month review of the CP5kTL, and maybe an important one.
With any, or at least, most other tires, this would not be news, but the GP5kTL will absolutely let go of the bead when the air-pressure drops below ~ 10lbs psi, so adding sealant is a bit problematic, as the old, dried sealant tends to get between the bead and rim in an irregular way, but alas, I had no choice.
While out riding a couple of months ago I ducked behind a shuttered restaurant, rolled through the parking lot to a discrete little nook, and relieved myself of some used Gatorade, not realizing that the shrub affording me privacy was a puncture vine, which I didn't realize until rolling across the parking lot to reenter the road from the other side.
I stopped as soon as I noticed, and was able to pull most of the needles out of the front tire before they penetrated, but they and a couple of patches of broken glass left me with a tire whose leak became something more than "slow".
As a remedy I decided to try adding 30 ml of Stan's Sealant to see if that would slow the leak so I could rely on a constant pressure throughout my rides. I have to say, to my surprise it worked quite well, but there are a few caveats if trying this.
First, is the tire worth saving? Mine was ~ 1/2 worn by the wear dimples depth, so in my case, yes. Second, I did everything I could to NOT disturb the bead while releasing the little remaining air, by turning the bike upside down so the wheel wasn't bearing any weight. Third, I used a CO2 cartridge to air up the tire as quickly as possible. Fourth, I used an injector that didn't seal the valve stem with the core removed.
I did lose a small amount of sealant, but slightly less than the normal amount, and put the full 110lbs or so of pressure in the tire to press the new sealant past the old. After sitting overnight I released most of the somewhat diminished pressure to purge the CO2, and aired up the tire with my floor pump.
I've ridden it a few times now and it's holding air much better, so I am pleasantly surprised this prodecure can, in fact, be done with the GP5kTL. The tire still has wet spots where the water from the original sealant seeps out, but it holds pressure well during my 2-3hr rides now. I really didn't think this would go well at all, so a very pleasant surprise.