I picked up an R1 engine the other day for my MNR.

The engine had been standing 3 years but came from a bike with under 3k miles.
There was paper blocking the inlet and exhaust ports but the water, oil and crankcase breather had been left open.

when draining the oil it was very thick, much thicker than fresh new oil and looked really brown. Choclaty brown almost.
I replaced the oil and done a compression and leak down test aswell as pressure tested the coolant system and the results where perfect..
210 psi on all 4 cylinders and very little leak down.

so I'm curious as to what you guys think made the oil turn creamy brown and really thick.
Can oil go off?

Moisture in the air will turn the oil manky (assuming the engine has been kept in a garage/outside/shed); similiar to when water/oil mixes in an engine.

Oil is made of compounds containing long chain molecules. You need a chemist to describe it but the compounds they break down into are not pleasant for an engine more like varnish. Oil should be changed every year.

Synthetic motor oil not only remains clean in use but is great for getting rid of varnish and gum in engines.

Yup just moisture due to standing for so long, Usually a gallon of flushing oil through it first before the good stuff does the trick. I would not recommend it but I have used a gallon of paraffin for a couple of minutes on an an engine that was particularly bad.

Just to add:
Be carefull what you flush the engine with as you can contaminate the clutch plates. I would just use a cheap engine oil as flush.