The crank plug oilway dropping out is a VERY occasional problem on this engine, but not enough to make anybody worry about it.
99.9% its the sender, which is a well known failure item after about four years of use. The diaphragm inside it deteriorates and the readings just get steadily lower.
Having replaced three on different engines and restored the readings on all three its the quickest engine rebuild in history
Once replaced you should see a very healthy reading on start up from cold..up to 3 to4 bar. Once the engine gets hot the reading will fall and you may only get about 1 bar at idle. Don't worry about this, provided the OP needle responds well when you rev the engine then all is well.