1976 FLH shovelhead ,Transmission oil foaming.

When I bought this bike a year ago the oil in the transmission was foamy or kinda yellowish it looked like to me. I assumed the previous owner used the wrong type of oil or wrong weight. I drained the oil and filled it with Harley gear oils which the dealer said was right. This month I refilled the trans and rode about 45 mph for 10 min or so. I rechecked the oil level and it was down about 3/4 inch and it was foamy. I found that the oil is leaking out around the seal in the main gear shaft. So my 2 problems are trans oil leak and something making the oil foam up. Can anyone out there think of what may be causing these problems? Any help is greatly appreciated and helpfull to us . Thank you every much. Big Nick