First of all, welcome to the hobby!

Second, I think its totally possible that the ramp flap rusted or oxidized or otherwise became discolored; 5 years in a warehouse will do that depending on conditions. The 'grease' I think is normal, was also on my steel I bought for new ramp flaps on my Taxi. (http://www.marcospecialties.com/pinball-parts/66-FSS006) .

Is it a problem? I mean probably not, but call your distributor, take a really good photo, ask questions. A good distributor will work with you, know the warranty terms, etc.