CA Gas Station - Lease option vs seller finance

[Saim Chaudhry]

I am representing a client with a gas station for sale in CA - the sellers have a potential buyer that they want to do a deal with. It is both the real property and the business that are to be sold. There is one major issue with this gas station that turns potential buyers off - they have underground tanks for their gas that need to be replaced with "double walls" instead of the outdated "single wall" tanks by 2025 per CA law or face being shut down. That is a large cost to a new buyer, and that is the main reason it has not sold as a regular transaction since it has been on the market. 

Instead of buying outright, the potential buyer my sellers brought has offered to do a lease option. Purchase the business for 50K, lease option the real property for 600K with a 2.5 year lease term and $3,500/month payments to the sellers. 

I want to ask, what would be most beneficial and protective option for the sellers...a lease option, seller finance, wrap around/AIDT or something alternative? I am worried that in 2 years the optionee doesn't upgrade the tanks and therefore doesn't exercise their option to purchase. Or they don't exercise their option for any other reason. That would leave the sellers with a defunct gas station that will most likely be shut down by the county for not having double wall tanks at that time. 

The second thing that worries me is if the buyer defaults during the lease period or decides not to exercise the option, the 1st DOT which is an assumable SBA loan will affect the sellers negatively because they are not going to have the money to upgrade the tanks and put it back on the market, therefore the SBA lender will foreclose since there is no income coming in to cover the monthly payments.

The thing I DO like about the lease option vs seller finance is that the Real Property remains under their name, so no need to go through a foreclosure if worse comes to worst and the optionee defaults. 

Any feedback or suggestions appreciated!