If the original cost is $100,000 and accum depr is $75,000, there will be a $75,000 ordinary gain on the sale from depreciation recapture. This will pass through on the K-1 as ordinary income. Normally, that would increase the retained earnings. From your post I am not sure if that gain is included in your RE calculation or not. If not, it should be added.
That would leave RE at $85,000. If the proceeds are distributed ($100,000), the distribution would come $85,000 from RE and $15,000 from PIC from an accounting standpoint.
The $100,000 is just shown as a distribution on the K-1 and on the 1120S. If that is the total activity for the year, the shareholder(s) would have $75,000 of ordinary income and $100,000 of distributions. The additional $25,000 is generally not taxable income.
If one or more shareholders bought their stock from someone else instead of it being issued by the corp, it is possible that the distribution will be "in excess of basis". If that is the case, it could cause additional income at the shareholder level.