I have a Volvo Penta seal very similar to the RMTA one, but no hose. Same as Jen-in-wellies. A cloth tied round the shaft stops enough water to allow the gland to be loosened, and the shaft to be inspected. I found the gland had worn grooves in the shaft, admittedly after several thousand hours. A slight movement of the shaft in the coupling improved leakage temporarily. I ended up replacing the shaft, cutless bearing and gland on a one day slipway pull out at Stafford Boat Club. If the prop shaft can be slid back far enough without fouling the rudder, just the gland could easily be replaced with a cloth round the shaft. My new gland came with a sleeve to allow it to be easily slid onto the shaft without damaging the seal lips.
The silicone grease really needs injecting between the two seal lips. A very fine tube on a syringe with an angle cut on the end allows the end of the tube to be manoeuvred past the front seal lip. Probably not a problem on the RMTA gland with the grease access on the top.
Richard