seal on bottom of air conditioner condenser is leaking, can that just be replaced or need a new condenser on a 1998 cadillac eldorado ?

I'm not familiar with a "seal" for the bottom of the condenser. The condenser is a one piece unit serviced as an assembly. If you are speaking of the lines going into and coming out of the condenser and the connection - yes, those lines and possibly o-rings may be serviceable. Either way, you will likely need professional help from a technician certified to legally handle refrigerants. Use this link to find some shops near you that can help with your concern: www.repairpal.com/repair-shops