I think my hozelock microbore system is the same as the one you are talking about, and I am having the same problem in that the t-joints to each dripper spur are leaking where I have pushed each microbore pipe onto the t-joint barb connector. The leaks into the plant tray are much more than the drips into the plant pots, and the consequent over watering is killing the plants. There seems no way to modify the connections to make them more water tight, so the issue must lie elsewhere. I wonder if pressure is too great (although I have the supplied pressure valve installed), or if having the system in full sun in a greenhouse is just too extreme and environment for the rubber pipe. I am waiting on hozelock to comment. I might try and fabricate a little sun hat for each joint. Unfortunately the problem varies per joint, so I can't just reduce the watering time to account for each leak.
There is another plumbing product called Fernox LSX. It's a silicone sealant, works against mains pressure. Some of the big DIY chains sell it if you don't have a plumbers merchants nearby.
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@Busy-Lizzie the original poster is still here. I was amazed when I saw the thread with my name against it. At least the content is still valid.