My LG LMVM1955SW suddenly started taking much longer to heat a few weeks ago. 4 cups of water would boil in under 10 minutes - would not boil in over 30 minutes. The water would get hot, but not boil.

Had a LG authorized professional come in to look at it.

He replaced the magnetron with a new one, and now the unit has improved, but it still takes about 20 minutes to boil 4 cups of water.

I'm not quite sure he knew what he was doing. He messed with the door, seems to have cracked the seal as he was trying to remove it. Its a hairline crack. Not sure how dangerous this is? He also did not do a leak test - which the service manual I found says needs to be done when any service is performed.

Any idea what could be causing the low power? Is this unit possibly dangerous with the seal issue?