Learn Finnish: Sitä ei korjattu vuosiin. - It was not fixed for years.

In Finnish, when you express how long something has not happened, you use the illative case. Vuosiin is the plural illative of vuosi (year). This is the standard rule for expressing duration in a negative sentence.

Why is the word for it in the partitive case (sitä) instead of the nominative (se)?

The action in this sentence is negative (ei korjattu). In Finnish, the object of a negative sentence must always be in the partitive case, so se becomes sitä.

What verb form is ei korjattu?

This is the negative past passive of the verb korjata (to fix). The passive voice is used because it does not specify who failed to fix the object, exactly like the English passive phrase was not fixed.

Could I use the singular form vuoteen instead?

Yes, but it changes the exact timeframe. Vuoteen is the singular illative, so Sitä ei korjattu vuoteen means it was not fixed for a year. Using the plural vuosiin means it was left unfixed for multiple years.