Fuel leaking is a hazmat emergency, call it in and let the DOT shut the company down. Or you might be treated or prosecuted as a accessory.
I really have nothing else to say except that you, as the agent of a company is responsible for checking a semi truck and seeing that it is adequately maintained for the loads you will be assigned to with it. If it is not, back to the shop it goes. With a stack of PTI write ups if necessary.
In the past Ive taken trucks and did work arounds for stuff that were broken etc. Later in my time out there Ive gotten very hard and expensive against a company that wont fix a truck. It's not acceptable. Either I have a truck that is in good condition and in good repair or I simply do not have a truck. Or even a job. It's very fundamental.
If a company clearly wont put money into a decaying fleet, do not work for them a day longer than you think that is the case. And let the state unemployment know this situation as well. Move on to a better employer.