You got a pretty sweet deal on that Strat... It's probably rusty because it was made in 1985 or 1986. Even the Mexican strats back in those days were about the same quality as the American ones... the myth that Mexican Strats are worse has grown and grown since that time period...

The way to identify the age of a Strat post CBS era by serial number is like this:

the serial number will start with a letter (if it's a mexican Strat it will start with an M...followed by the decade code) which represents the decade

s - for 1970's
e - for 1980's
n - for 1990's
z - for 2000's

Then the next letter represents the specific year

e5 - 1985.

I'm not exactly sure when they added the M for Mexican code somewhere in the late 80's I believe... but nowadays if you see a Strat that has a code of MZ2XXXX it's because it's a Mexican. US strat serial numbers start immediately with the decade code.

The 1980 Fender strats weren't in very high deman so it's harder to date them. Some Strats can be from up to 3 years AFTER their serial number date. Just depending on how many Strats were made in that specific year. Instead of using all new decals, Fender would use the left over decals from the year/years before...