MANAMA, Bahrain - Lewis Hamilton warned on Sunday that his McLaren team must investigate and fix pit-stop problems before any bid for the World championship is wrecked.The 27-year-old Briton was eighth in the 2012 Bahrain GP despite two sluggish pit stops during which his pit crew had problems with the left rear wheel-nut; the previous week in China a bad wheel change cost team mate Jenson Button his chance of winning.Hamilton said the team's stops were a serious concern and threatened championship success.SERIOUS CONCERN"We need to look into this very seriously. There has to be an investigation because we gave away a lot of points again today (Sunday) - that's how championships are lost. We have to make sure we pick up in the next race because we can't afford to lose points like we did today."Seasoned observers estimated that the two bungled stops cost Hamilton around 18 seconds in Sunday's race - enough time for him to have finished much higher up the field and to have kept his lead in this year's title race.Defending double World champion Sebastian Vettel (Red Bull) won on Sunday for the first time in 2012 but Hamilton shrugged disappointment aside: "It's motor racing. I had no idea what went on but I was hoping the second time I came in that I wouldn't have that problem, or I was hoping that it would be a good pit stop but it was exactly the same, if not a little bit longer than the previous one!"We still picked up some points - I've got to be happy with that. There weren't many positives for me - just the four points. My pace wasn't great - I was really struggling to look after my rear tyres."'DIFFICULT WEEKEND'Button said he had no idea why the team was so off the pace after starting the weekend as favourites. "We were really struggling with oversteer and all the way through the race we were taking front-end out of the car, but we just didn't have the pace here and we don't know where it's gone."It's very difficult to understand where the pace is and why we didn't have it around here. In the last races, whether we've won or not, we have had good race pace but we just didn't have it here."So, a difficult weekend for the team."