Oil flow - my sump is definitely dry!

[misterdimwiddy]

I occasionally see posts from new TRX owners that question how to reliably check the oil level on this dry sump motor and think, "it's not so hard when you know how".

It therefore surprised me today to come up against some strange behaviour when firing my TRX up after lots of winter work I will outline the sequence of events as briefly as I can below;

VW oil pressure switch fitted last summer
Always showed red below 2krpm when the motor was hot but took this as switching pressure being incorrect for this motor
Moved switch from head down to crankcase end of oil pipe (forum advice)
Improved to a degree but still illuminating at low revs when stinking hot
Removed sump to check oil pickup strainer was not blocked with crud causing low pressure
No crud found and so sump replaced carefully checking various O-rings for correct installation
New oil and filter added
Months pass by................before start up
Fire it up today to check everything works before Brands in April
Awful rattly sounding motor (even with a loud end can) and oil light on permanently! (it never shows when running cold)
Turn it off quickly and scratch my head
Noticed Oil level in tank did not drop when the motor ran briefly; usually does drop as oil circulates
Suspect piss poor oil flow; confirmed by no flow from 6mm head bleed bolt
Remove both sump plugs; NOTHING from crankcase and slow flow draining tank on M10 filter housing bolt. There were at least 3 litres of the stuff somewhere.
Curse loudly and remove sump again; filter was bone dry showing no flow from at least one pump. Filter was in the right way up!
Nothing obviously out of place internally
Reassemble, refill oil and fire it up again while visibly cringing
Oil light went out immediately, sweet sounding motor as usual and rapid copious oil flow from 6mm head bleed point (always used to be just a trickle which I never understood; think its gravity fed not at pump pressure)

So all seems OK but the trouble is I have no idea what I have corrected.
Maybe internal oil passage leak (displaced O-ring within sump?) causing no flow to the head (would expect oil to drain from sump bolt and it did not); air lock (not sure how this would occur or why pump would not be gravity fed from tank.

I'll probably never know but any thoughts or similar experience would be welcomed

Does make me aware of the risk of errors and over sights when doing work over a long period of time. Things can easily be left loose or absent; (recent post about loose caliper bolts). Must check her over thoroughly before my first spring outing.

[HansJ]

No hints on what can have happened, but that's the reason why i always run the engine on the starter without plugs (or if I'm lazy, just disconnected plugcables), to make sure that oil is dripping out from the tell-hole in the head.

And i agree with long-stretched repairs. You always think: "I'll remember that, no probs". Yeah right... I try to scribble down things that i need to do, but i forget that as well...