Is there a lawyer in the house?
While insurance will cover most things, and most excesses are low enough that anyone flying should be able to cover the costs, there may be situations that are not so cut and dry.
For example, say a member racks up a £25K landing fees, instrument approach and parking fees at a major regional international airport over a month (or at Luton for an emergency diversion) and convinces the operator that the syndicate will pay on invoice served at end of month (or just leaves it there) and they have moved to a non-EU foreign country (not that moving to an EU country will matter anymore) or sold off their share? Who coughs up the £25K? These sorts of debts generally move with the airframe, so regardless of what any agreement says, you're all probably in for an equal share of remediation before they impound your aircraft.
Say, after a forced landing from an engine failure, not only do you take out a kindergarten and both the generator and mains supply to an emergency hospital causing deaths of many - but you also take out a puppy farm. Your syndicate's 3rd party insurance may be limited to, say £10m, but the puppies took the damages to £20m.. The syndicate owes £10m... While you could have handled the forced landing slightly better, the engine failure is hardly your fault (alone) in a syndicate.. so should you pay for it all just because the engine quite while you were flying it? In this case, though, I think the pilot is strictly liable (which is odd, as this is a form of criminal liability) for third party losses and has to cough up - too bad that the person in the syndicate who is responsible for maintenance has been faking themaintenance invoices and sticking the banana peel into the crank to keep the crankshaft quiet... Although, you could probably sue that person for damages...
Then there is the situation where, thankfully, no third party or property was damaged in the accident, however, at the last few metres of the forced landing roll, you hit a ditch and it ends over and they have to cut you out. The a/c was insured for say, £50K and you get all of it back.. However, for some reason, you can't find a like for like for less than 75K (and the idea of getting a shabby version and bringing it up to spec is not economically viable). Who coughs up the additional £25K. Again, it is not your fault that the landing area you chose had a ditch which was invisible from the air - and up until you hit the invisible ditch, everything was done better than by the book.. And of course, it is not your fault the engine quite. I am not sure, just because the syndicate rules say that whoever is at the controls of the plane at the time is liable, that the person at the controls will be liable if it went to any legal process.. and for £25K, it may well go there...
There is a difference between coughing up a few hundred or a thousand pounds for excess (but even that can be dicey) versus many thousands, hundreds of thousands or millions... If you have a partner who you absolutely trust, it may be worth transferring all your assets into your partner's name.. How much you could trust your partner after the transfer will probably be inversly correlated to the amount of assets you have just transferred. In other words, if you're a pilot, you're screwed either way.
Also - in the above scenarios, assume no amount of preflight would identify the cause of the failure... without a lot of tools and a licence where required.
[edit] For the purposes of liability, Luton did not charge the PA28 (from memory) thaty performed an emergency diversion £25K.. I think it was closer to £1.5K.. That comment was to highlight the regrettable decision of Luton not to join the Strasser Scheme...
[edit again] For a limited company, you may have your liability limited to the unpaid capital (e.g. £2 for a £2 company), however, if insurance pays out on the hull, the company will have to hand that over to debtors, any shortfall in the 3rd party claims would probably have to be picked up by the pilot and not the syndicate (I think... although I understand there are precedents where the pilot was the first port of call and then the operator - maybe not here) and if a member who was at the controls at the time digs their heels in and will only pay in proportion to their shareholding, will you risk losing say a £100k plane for a £25K debt? You would probably turf the member form the syndicate, sell the share and distribute the proceeds to the members who paid...