eclipse 12 812dvc problem

i have an 12" aluminum dvc eclipse sub that was hitting in the mid 130's right now it is only hitting in the mid to low 120's. the excursion on it is the same as when it was in the 130's. its rated at 500watts rms and i am giving it 400. it is in a sealed box and had blown out some of the seals(i folded the carpet in the box in 2 spots). i resealed it yesterday with a generous amount of silicone. any ideas why i would be getting a 10db drop even though the excursion is the same? btw, it is a jl amp

measure your resistance on the coils maybe you have fried one of them, but sounds more like a leaky enclosure,    look around the box to see if there is any other leaks2009 0-1000 Trunk WR 154.0DB 2009 1001+ Trunk WR

2007 USACI World Champion

2007 World Record

2006 USACI Finals 2nd Place

i sealed every edge with a 1/4" thick bead of silicone and smoothed it out. it has a rubber surround and is in perfect condition. sub is only 2 monthes old. i didnt have time to pull the sub out of the box and check each coil, but i would assume if one was cooked the excursion would be much smaller. the sub has 2 4ohm vice coils running in paralell for a 2ohm load on the amp if that helps any. i doubt i blew the sub because i am underpowering it unless jl underrates their amps more than i thought.

even with one coil blown most subs can still reach full excursion2009 0-1000 Trunk WR 154.0DB 2009 1001+ Trunk WR

2007 USACI World Champion

2007 World Record

2006 USACI Finals 2nd Place

what could have made the coil blow(am going to check them in the morning)? i had adjusted the gain with a dmm and a sine wave to 400 watts when sub's recommended is 500rms. 28 volts at 2ohms. 31v at 4ohms. also i have a pretty good ear so i would never go up to any level of audible distortion. it is an sq system and i usually only listen to rock so i rarely pushed the sub. the rare times i did were only for a short period of time showing off with some bass test cd's. the sub is definately blown anyways, any suggestions on a sub that will work well in a decently sized ported enclosure that will work well with 400rms and can be pushed to mid/high 130s db? i have a single cab pickup and the sub will be where the center seat/console was so it will need to pretty good on the sq front too. i would get a more powerful amp. but i have 2 other amps for my components and am very pressed on amps. cannot afford a new alternator on top of a new amp and sub