Need help with a thermal paste choice

[Breaker]

Greetigs!

I met a very wierd problem lately: quick thermal paste degradation, while applied under a 5w cree diode chip, the chip itself is nothing special, the only problem is that the temperature underneath in a working state is arround 80-90 deg. C ,and usualy the chip works like 12 hours a day, 7 days a week

AS5 degrades in a week,cheap Evercool paste work a bit better,MX4 works for 2 weeks or so,the best i have discoreved so far is MX2, but even so, it lasts only for a month..... then, all of them dry like a desert sand... and of course if i dont replace it, the chip dies....the probem comes from tha fact that i am talking about 58 chips, and it`s hella booring to renew the paste every month
Wonder though, why this thing even happenes when even the cheap Evercool paste clains to be stable at 130-140 deg C

Any solutution?An thermal recommendations?(sadly,i cant use bigger headsinks,no room)

P.S

Was thinking about liquid metal, but the cooling chip console is made of aluminium, and cant be swapped with copper one, the whole cooling body will became heavy

 

[pigpottomus]

You can try Artic Silver 5?

 

[RnRollie]

bleh AS5 isn't it
Prolimatec PK-1/3 or Gelid
Though, you might be better off with some thermal glue/epoxy

I think its not the temps which are causing the issue... How "exposed" to air are these things?

 

[EarthDog]

AS5 does not degrade in a week. There will be THOUSANDS of people just at this site telling you otherwise.

As RnR said, how exposed to the air is the paste that it is drying out? Under a 'normal' circumstance, like under a heatsink, people do not replace the TIM for YEARS... so I am wondering if it is the environment it is exposed to which is not appropriate for paste...