righto, replace ALL the seals and try it, if it still leaks get a 2nd hand dizzy and swap the shaft (your shafts probably gouged) you can try machining the shaft down a bit but thats not really a perminant fix.
As for a replacement, keep an eye on trademe and here on toyspeed for anyone selling engines or engine parts and just try asking them to sell seperatly, i got one for $20
oh yea, theres 2 seals along the shaft i think, I did the same as you and replaced one and found that it still leaked a bit, AND replace the bearing with a new one, it'll be pretty worn by now after having all the oil washing thorugh it.
A plan so good my head would explode if I even began to know what I was talking about...