300tdi engine kept turning over when key removed

hi all
hoping you can all help me out
95 disco - turning ignition causing engine to turn over which fails to stop when key removed - instant battery drain (after approx 20 seconds) of engine continually turning over - and upon opening bonnet a small glow of fire on bottom right hand side of engine

I'm obviously new to this mechanical stuff and discos but a mate tells me it is most likely the stater solenoid sticking which causes instant drain and gets that hot that it combusts

if he is right (which I have no reason to doubt) should I just go down the road of new starter motor or is there anything else i should investigate before purchasing

apologises as it is my first post but I only bought it 3 weeks ago and haven't had time to signup before but NOW I have a real need

Right hand side looking over the radiator from outside the car?
Sits aprox 2 thirds down from the top of the engine hidden in the transmission tunnel

My guess is starter is creamed

eBay is £88 plus postage I think or you could take it off and take to an auto electrics company but i doubt they would be able to repair for much cheaper!

Seen it happen umpteen times on all sorts of engines, bang a new starter motor onit bud.

thnakyou both for taking the time to feedback and yes upon openign bonnet there was a small glow of fire on right hand side down by tunnel (quick blow blew it out so i would guess it was plastic smouldering judging by the smell) - sounds like my mate was right and new starter required as im guessign the soleniod plastic end caught light - woudl this cause the battery to flatten within seconds and is it something easy for a novice disco owner who has some mechanical experiance

Changing a starter motor is easy, but remember to disconnect the battery first. Will give you quite a spark if your spanner touches the live terminal and earth.

Advice again Im afraid - Paddocks starter replacement as good as anywhere else? (£100 inc the vat)

you were both right - ordered new starter motor and replaced on saturday (I also suffered with the apparenet difficulty of getting to top back bolt - long extension and accessign behind manifold did the trick) fires up instantly now - thanks for advice