I have the Fender 7250ML super bass long scale bass strings. I had them for two years now. I just bought some rotosound 66 swing bass strings but i don't know if i should use them yet. The strings I have now seem to be a bit dirty. Should I just clean them or replace them?
That is entirely up to you. Some folks like a more dead/less lively tone. Others like the brand new string thing. The guy you're named after tends to be a "brand new string" type.
The current strings on the bass are nickel plated steel roundwounds. I suggest replacing them. Take off the old strings carefully though - you can generally pop them back in if you want. The tone will probably be MUCH different than you are used to. I have never experienced any type of roundwound string to really LAST and continue giving great note definition past 3 months of moderate to heavy use. More like one month of heavy use....