Whoever prayed then remembered that they forgot a limb in wudu, should simply go back and wash that limb then redo that prayer. If they forgot a sunna of wudu, they do not repeat the prayer. He will just do that sunna for the future prayers.
َمْنَ تَرَكَ فْرًضا مِْنَ فَرائِض اْلُوُضوِءَ فإَِّنُهَ يْأتِي بِِهُ ثَّمُ يِعيُد الَّصلاََة،َ وَمْنَ تَرَك سُنَّةَ فإَِّنُهَِ لاُ يِعيُد الَّصلاََة،َ وَيْفَعُل تِْلَك الُسنََّة لَِماُ يْسَتْقَبُل مَِن الَّصَلَواِت
Source: Matn al-‘Iziyya
Written by: Shadee Elmasry
Study Maliki fiqh at Arkview.org.