Starter motor, 300tdi, wouldn't disengage now OK Advice please.

As in the title. Defender 90 300tdi 1996.
Lucy has been starting and driving fine. I stopped her outside a friends house for a few minutes and then set off again. I had an additional noise. It could have been the belt slipping or a split pipe. I pulled over and had a look. Could still hear this noise. Drove a but further and noticed smoke from the engine bay. I pulled over and switched off. Something carried on running for a few seconds. Opened the bonnet. Smoke and electrical burning smell. After a few minutes I tried to start her again but got absolutely nothing. She wasn't even trying to turn over. After waiting about 40 mins she started. There was the same noise so I switched her off again. The noise carried on for a few seconds.
Called the AA out and he immediately diagnosed that the starter motor wasn't disengaging. He offered me the options of giving me a tow start or towing me to a garage (before telling me that he couldn't tow me as he had nowhere to attach to. Note to self - get those jate rings you keep almost ordering you idiot). Whilst I was waiting for the recovery truck, a car that was parked behind me moved. I had just enough room to roll back and bump start her in reverse. Happy days - After calling the AA to cancel the recovery truck I drove home. .
Now she starts fine again. I've been for a drive and stopped on a few hills and turned her off. Starts on the button every time.
I'd like to ask the opinions of the good folk of LandyZone.
Do I take it as a one off jam and carry on driving her.
Do I replace the starter solenoid.
Do I replace the Starter Motor
Could it be the ignition switch and not the solenoid or starter.
If I replace the Starter motor do I go after market for £85 or OEM for £190
Over to you fellow LandyZoners
Antony

I'd take the starter off first and see if it's simply gunked up in the nose area .. Might just need a clean. However, bearing in mind the smell and smoke I'd replace the wiring to it. There's likely to be siugns of burning on the wiring so it ought to be easy (Heheheh) to spot ... (Nowt's ever that easy with Landies)

Paul D said:

I'd take the starter off first and see if it's simply gunked up in the nose area .. Might just need a clean. However, bearing in mind the smell and smoke I'd replace the wiring to it. There's likely to be siugns of burning on the wiring so it ought to be easy (Heheheh) to spot ... (Nowt's ever that easy with Landies)

Click to expand...

That's got to be step one then. I'll take it off check and clean it and check out the wires to it with a view to replacing them.
Cheers Paul.

Update - Starter was working fine and the wiring checked out ok. I then got an intermittent fault. If, for example, I stopped at the shop on the way home from work, occasionally when I came to start her again there would be nothing other than the click of a relay. Leave her there and walk home. Go back an hour later and she'd start straight away. If I'd stopped on a hill I could bump start her. Once bump started and switched off again she would start ok. Took the starter off, cleaned the end. Opened the solenoid and made sure that it was moving freely, cleaned the contacts and refitted. Problem went away. It started happening again last week so I ordered a new starter motor. Part number ERR5009N from Paddock. I ordered the N thinking that it would be a brand other that Britpart and because it was in stock. Anyway the box it arrived in was brown not blue. It did however have the Britpart logo all over it. So my new starter motor is Britpart. I fitted it anyway. Two days in and so far I'm impressed by the power of it. My Landy is starting far more quickly that it ever did (and everytime). As for longevity...... I'll keep you posted.