Growth requires resistance. Without resistance, there is no addition of potential. So when it comes to GMAT preparation, if you come across a difficult problem, seeking solution immediately is stopping yourself to grow out of that problem.
When you come across a problem, your mind starts to find solutions to that problem. You should gift your mind that opportunity. After brainstorming, if you seek help, then it is going to be branded in your mind forever. Also the mind has its share of exercise and practice. This is the way to learn any trade and making it the second nature.
Personally for me, Mathematics is my second nature and I do not have to exert myself or brood over math problems. But for Sentence Correction, I sometimes spend up to 30 minutes on a single problem and still ends up being unsure of the answer. It is because its various rules are still not itched into my memory and to burn them I need to bear the pain of thinking hard. So basically I try not to seek the solutions and instead try my level best to come with an answer with an explanation. After that, when I see the solution, there is an AHA moment and the learning remains with me forever :)