Disappearing LSD

[helievacpilot]

My 96 axle code is D5, which is supposed to be 4.10 lsd. When I changed the fluid, it appears that the PO ditched the lsd and just put in an open diff. It's a stock 2wd quad cab dually. Would like to replace it, but don't want to break the bank. Are there any "lunch-box" lockers for this application or should I look for a factory unit on e-bay?
Thanks - Bill

[alberta 7.3]

Powertrax sells a Lock-Right to fit the 10.25 rear

[helievacpilot]

Thanks, I'll check it out.