Hi, I'm swooping the MR16 halogens for LED. The body of the new lamp is slightly bigger and I've managed to fit 5 of them but the 6th has beaten me. I can't shove it in far enough to get the retaining circlip to stay on. Any suggestions welcome. There is no obvious obstruction, I've cleaned the groove out, tried a bit more force, but it just won't sit in. Thanks.