You will need a new antenna, but they make adaptors for the transducer I believe. You will need an adaptor to go from your gray or black ducer/power plug to a newer red/blue one, depending on what newer unit you buy. The GPS antenna and receivers are totally dif. You should look at the color Eagle units available right now as well. They are made by lowrance and will cost less $$$$.
The adaptors are on ebay for cheap, btw. I’d call lowrance’s customer service to get yourself a possible rebate coupon (discount off a new lowrance since yours cannot be fixed) and also to inquire about specific parts needed to hook your ducer up to a new unit. You may want to just get the new ducer and all with the new unit. The dif. in cost is not much. Also, a new unit with internal antenna will solve your antenna compatibility concerns. The internal antenna in the red connector units (that would use LGC-3000 antennas) is said to be much more reliable than the external LGC-3000 antenna.