XP: Graco Nautilus install question

memali26

Posted this over on nurseries and gear, but I think this board gets more traffic so I'm XPing... 

We have DD1 harnessed in the Graco Nautilus. She's been in it about 4-5 months and I've loved it until now. It's installed with the LATCH, both upper and lower anchors, per the instruction manual. Over the last several weeks I've noticed that it doesn't seem to stay installed tightly - like the LATCH belts are loosening - and we've had to re-install it several times to make sure it's in properly.

I'm wondering if this is a typical problem with the Nautilus (I never saw it mentioned in the reviews I read before buying)? Or a defect in our specific seat? Is there anything we can try to fix it, or just install with the seat belt and see if that's better?