If im posting this in the wrong place my apologies its my first post just getting used to the site

I have a problem with my 2001 (y) omega 2.6 (y26se) it was running like a pig for about a month i parted with a £100 to my mechanic who first told me to burn it (cheeky sod) then spent four hours cleaning breathers and checking codes on ECU, he almost got it to run ok not great but as soon as i got 50 yards from the garage it started again (as soon as it was under load) - revving to 2000 revs then dropping waits a second then repeats also missing badly when cold i solved this two weeks ago and quite honestly its driven like a new car (i unplugged maff its been unplugged for two weeks now). as i drove to a set of traffic lights last night i get a loud whining sound from gearbox as i stopped car it stalled i tried to restart with no luck the only way i can start it is to hold accelerator to floor i have to continue to floor accelerator soon as i let pedal off it stalls it revs at 200 maximum yes 200 folks! and it wont rev any further, exhaust bangs and rattles and whole car shakes whole engine knocking badly also noticed a quarter of and inch of mayo on oil filler cap and oil filler pipe (no oil in water or on dipstick) did not overheat before it died temp was at 83 first problem i knew of was the whining from gearbox it ran like a dream up untill that moment i dont know where to start looking

and would appreciate any help at all please excuse my typing im half asleep lol thanks in advance