I dont have much time in on the old landy engine, but I've worked on the marine version, I must say I find it very odd that the crank pulley would have any relationship to this problem.
Maybe theres an oilway on the end of the crank or something and the pulley covers it, if that was the case I'd expect your landy to be making a bigger oil patch than normal.
Sure one of the other guys will be along soon with some more info.