Daimler double six 1994 - transmission question

Hi- I’m in the UK and will be soon selling a DD6 6-litre for a friend of mine. It has 2 issues with the gearbox that need fixing first though, and I was wondering if anyone else had had these issues. Firstly, while in park, you sometimes have to wiggle the gear stick for it to start. I read somewhere that it could be due to a decoder box near the gearbox that needs attention? And secondly, from a cold start, while in drive it doesn’t change up gear unless you stop, turn off the engine, and turn back on then it’s fine. Would be great to hear from anyone who’s had these issues, thanks!