Like the previous guys have said, you can replace the clutch pressure plate either way - engine in or out. Both methods require removing the floorboards - lots of dismantling either way. I vote for pulling the engine, especially if you're going to tackle other issues. It's really easy to replace the clutch parts with both trannie and engine sitting on the garage floor. In addition to the friction plate, replace the pressure plate, release bearing, pilot bushing, as well as having the flywheel friction face refinished. Easy to do this now when it's all apart and they all do wear out over time.
If you don't go for the Moss rear seal kit, do install the modern crankshaft front lip seal. Easy to do. Even under ideal setup, the original rear seal design will leak, hence the crankshaft scroll. The only variable is how much. You didn't specify what kind of oil you're using, or if it changed just before the leak increased, but the "T" series motor experts all recommend a mineral-based 20W50 oil. Pouring synthetic oils into these ancient designs will create seeps and leaks in places you've never seen it leak before. Synthetic oils are great lubrication products, but won't stay in the motor long enough to be of benefit.