During several of my recent marker rebuilds I’ve needed to fix leaks in macro lines. Most of these leaks were caused by worn or deformed o-rings in the fittings and not the hose itself.
Replacing the o-rings is pretty simple too. Just place a drop of synthetic oil between the body and the collar and rotate it to work the oil into the fitting. Next use a flat bladed screwdriver to pop the collar off the fitting. The o-ring can then be easily removed using an o-ring pick. Now clean and fit a new number 10 o-ring before clipping the collar back into position. Job done!
To prevent damage to the new o-ring make sure that there are no sharp edges on the macro line before re-inserting. I also lightly lube the end of the macro line with silicone marker lube. But don’t use too much as it will hold dirt and grit which can get into the fitting if you need to remove the macro line in the field.