dont use glue, its actually fairly easy job,
and what ever you do don't stretch it, if any thing try to compress it as fitting it,
the alloy clamps at the top should only be loosened not removed, and the studs in the corners inside the lamp hole snap easy as,
please do not use any kind of petroleum lubricant on the seal you will shorten its life dramatically, but dash shine is fine as it contains loads of plasticisers that will help the rubber live longer, and its dam slippery
when I fitted they 5 or 6 I have done for others I discovered that no lube is best, as once in the seal stays in place as you try to refit the bumper, once reattached try no to over tighten the fixings at the top as the seal squashes too much and you can see it when you look across the rear of the car,
once fully installed cut your little soft alloy bar in half push up the inside of the seal each end, then fold round the arch,
the front is much harder to get right