Technically it does NOT reduce your basis as much as it adjusts it.
When you sell any property that was being depreciated(using the 179 deduction, the regular or special depreciation options), the depreciation is always recaptured and taxed at a rate of no more than 25%. This portion reduces your cap gains so only the gains above the recaptured amounts get the preferred cap gain treatment.
You MUST take some kind of depreciation on an asset ... it is a requirement not a choice. The only choice you have is how fast you can depreciate the cost. If you have not properly been depreciating a property then seek out local professional guidance to get the massive error corrected ASAP.
When you sell a rental property is special bonus depreciation reduce your basis for gain loss purposes?
In a sense, yes. All depreciation is recaptured and taxed in the tax year you sell the property.
What about section 179?
What kind of rental property is this? It matters, because residential rental real estate is not eligible for any SEC179 deduction. But some assets are eligible for the Special Depreciation Allowance.
Repairs?
While depreciation is on line 18 of the SCH E, repairs are an expense that are included on line 14 of the SCH E. Once repairs are claimed/deducted, that's it. The deduction is permanent, while depreciation of any type is not permanent.