Smoke at startup is not unusual for a 90. They do not have valve stem seals. Highly unlikely rings are an issue, very rare to see ring issues even at very high miles. Worse case the lower injector housing seals are leaking. A relatively easy fix. As me how I know. Price is a bit high for a 52k mile 90’. Looks very clean, but without a detailed service history I wouldn’t bid over $17k for that car. Good luck.
H
