It will cause issues if it's leaking, but is highly unlikely to cause 'limp mode'. You would hear an obvious 'whooshing sound' when it came on boost if it was leaking. Definitely swap it even if it's not leaking (because it soon will be), but don't go to Ford - Get a silicone one from eBay. I guarentee it will last longer. The Ford ones can fail within a year.

Also the vac operated EGRs can't flag any fault codes, or bring on limp mode - only the Euro4 electrical ones can.