Stained laminar flow HEPA filter question

[BorisValetto]

Hi to all!

Maybe some kind soul can help me out: ive recently bought a used laminar flow hood. Everything looks great, except the HEPA seems to have a huge humidity stain (i don´t know if thats the right word... it has a big sort of brown stain)...

as the vendor told me, its been sitting in a garage for like 15 years... everything works great and it was a real bargain, im just wondering if i should change the hepa for a brand new one or the stain will not be a problem...

i can post a photo too... please help! it will be greatly appreciated! excuse my english :P

best regards