Unfortunately, you need a new contactor assembly. These 200 amp switches are not rated for 200 amp continuously. Cleaning the contacts usually makes them worse.
A voltage drop test will tell you how bad it is. With the utility on and feeding the house, put your vom in ac volts and put one probe on the bottom of the breaker and the other probe on the load lug on the same side. You should read 0 volts. 10, 20 or 30 millivolts may be acceptable. When you start seeing 1/4 volt or 1 volt, then there is too much resistance across the contactor. You can then transfer it (generator running and load connected) and read voltage drop from the generator lug to the load on the same side. But the problem is most often on the utility side as it's in use 99% of the time. Voltage drop has to be read only on a closed circuit that also has current flowing in it. You can read this across a circuit breaker as well as across any suspected resistance. We see these overheated contactors on houses that have heavy normal electric loads such as 2 or more electric furnaces, electric water heaters, multiple air conditioners. You have to keep your utility load down to prevent this overheating of the switch. If you can't keep the everyday load down, then a 400 amp switch is the only solution and that's expensive. A contactor should last about ten years, but 2 or 3 in ten years will need a bigger switch. That movable blade that is not in contact with the upper contact is because the plastic has melted that holds that blade due to temperatures caused by sustained high ampere loads That or you'll just have to turn off your grow lights. I'm pretty sure the part number will be 0L2911
State your problem, not your diagnosis.