Well, Bud...something naggin at me that I want to share but the words don't come...I keep editing. It still won't be 'right' but I throw it out there for thought...
Simply said, I've known many of the old school like your dad who felt their sins mired them in guilt. I myself have only come to truly understand "grace" in the past decade...up till then, my religious teachings emphasized "earning our salvation." That makes "self forgiveness" terribly hard to achieve... even if we accept Christ as our beloved Savior.
Some take the word so literally, that even though we all are destined to sin anew these folks tend to beat themselves down that they're not totally without sin. I know why God sent his Son...because I and most I know, just can't get it right on our own and we're conceived in Sin and will continue to Sin. Only through the Holy Spirit working in us can we begin to undo that and improve...but only in death before Christ will we be made perfect!
Maybe like so many of the older folks I've known, your dad is like that?
God is omnisicent and often we're right where God needs us to be in our walk.
I will still pray for your Dad to enjoy the "joy" promised us from embracing our sins being washed clean, but I won't specualte on whether his salvation is tied to that. Only God knows his heart...
May the Holy Spirit move to "open the eyes of your dad's heart" and see Jesus as He truly is!